Guanylate kinase;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  147 YSRPVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLY 223
Cdd:pfam00625   1 SRRPVVLSGPSgvgKSHIKKALLSEYPDKFGYSVPHTTRPPRKGEVDGKDYYFV-SKEEMERDISANEFLEYAQFSGNMY 79

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  224 GTSVQSVREVAEKGKHCILDVSGNAIKRLQLAQLYPIAVFIKPKSVENILEMNKRLMEEQGRKTYDRAMKLEQEFLE-HF 302
Cdd:pfam00625  80 GTSVETIEQIHEQGKIVILDVDPQGVKQLRKAELSPISVFIKPPSLKVLQRRLKGRGKEQEEKINKRMAAAEQEFQHyEF 159

                         170       180
                  ....*....|....*....|...
gi 528482432  303 TAIVQGDTLEEIYNQVKQIIEEQ 325
Cdd:pfam00625 160 DVIIVNDDLEEAYKKLKEALEAE 182

Guanylate kinase;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  147 YSRPVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLY 223
Cdd:pfam00625   1 SRRPVVLSGPSgvgKSHIKKALLSEYPDKFGYSVPHTTRPPRKGEVDGKDYYFV-SKEEMERDISANEFLEYAQFSGNMY 79

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  224 GTSVQSVREVAEKGKHCILDVSGNAIKRLQLAQLYPIAVFIKPKSVENILEMNKRLMEEQGRKTYDRAMKLEQEFLE-HF 302
Cdd:pfam00625  80 GTSVETIEQIHEQGKIVILDVDPQGVKQLRKAELSPISVFIKPPSLKVLQRRLKGRGKEQEEKINKRMAAAEQEFQHyEF 159

                         170       180
                  ....*....|....*....|...
gi 528482432  303 TAIVQGDTLEEIYNQVKQIIEEQ 325
Cdd:pfam00625 160 DVIIVNDDLEEAYKKLKEALEAE 182

Src Homology 3 domain of Disks large homolog proteins; The DLG-like proteins are scaffolding proteins that cluster at synapses and are also called PSD (postsynaptic density)-95 proteins or SAPs (synapse-associated proteins). They play important roles in synaptic development and plasticity, cell polarity, migration and proliferation. They are members of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. DLG-like proteins contain three PDZ domains and varying N-terminal regions. All DLG proteins exist as alternatively-spliced isoforms. Vertebrates contain four DLG proteins from different genes, called DLG1-4. DLG4 and DLG2 are found predominantly at postsynaptic sites and they mediate surface ion channel and receptor clustering. DLG3 is found axons and some presynaptic terminals. DLG1 interacts with AMPA-type glutamate receptors and is critical in their maturation and delivery to synapses. The SH3 domain of DLG4 binds and clusters the kainate subgroup of glutamate receptors via two proline-rich sequences in their C-terminal tail. It also binds AKAP79/150 (A-kinase anchoring protein). SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 528482432  22 YVRALFDYDITKDSGLPSQGLNFRFGDILHVLNASDEEWWQARHVTTDGEMEEMGVIPSKK 82
Cdd:cd11861    1 YVRALFDYDPSRDSGLPSQGLSFKFGDILHVTNASDDEWWQARRVTPNGEEEEVGVIPSKR 61

Guanosine monophosphate kinase (GMPK, EC 2.7.4.8), also known as guanylate kinase (GKase), catalyzes the reversible phosphoryl transfer from adenosine triphosphate (ATP) to guanosine monophosphate (GMP) to yield adenosine diphosphate (ADP) and guanosine diphosphate (GDP). It plays an essential role in the biosynthesis of guanosine triphosphate (GTP). This enzyme is also important for the activation of some antiviral and anticancer agents, such as acyclovir, ganciclovir, carbovir, and thiopurines.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 150 PVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLYGTS 226
Cdd:cd00071    1 LIVLSGPSgvgKSTLLKRLLEEFDPNFGFSVSHTTRKPRPGEVDGVDYHFV-SKEEFERLIENGEFLEWAEFHGNYYGTS 79

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 528482432 227 VQSVREVAEKGKHCILDVSGNAIKRLQLAQLYPIAVFIKP 266
Cdd:cd00071   80 KAAVEEALAEGKIVILEIDVQGARQVKKSYPDAVSIFILP 119

Guanylate kinase [Nucleotide transport and metabolism];

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 177 VPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLYGTSVQSVREVAEKGKHCIL--DVSGnAikrLQL 254
Cdd:COG0194   33 VSATTRPPRPGEVDGVDYHFV-SREEFERMIENGEFLEWAEVHGNYYGTPKAEVEEALAAGKDVLLeiDVQG-A---RQV 107

                         90       100       110       120       130       140       150       160
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 255 AQLYP--IAVFIKPKSVEnilEMNKRLMeeqGRKTYD--------RAMKLEQEFLEHFTAIVQGDTLEEIYNQVKQIIEE 324
Cdd:COG0194  108 KKKFPdaVSIFILPPSLE---ELERRLR---GRGTDSeevierrlAKAREELAHADEFDYVVVNDDLDRAVEELKAIIRA 181

                 .
gi 528482432 325 Q 325
Cdd:COG0194  182 E 182

SH3 domain; SH3 (Src homology 3) domains are often indicative of a protein involved in signal transduction related to cytoskeletal organization. First described in the Src cytoplasmic tyrosine kinase. The structure is a partly opened beta barrel.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|....*..
gi 528482432   24 RALFDYDITKDSGLPsqglnFRFGDILHVLNASDEEWWQARhVTTDGEmeemGVIPS 80
Cdd:pfam00018   1 VALYDYTAQEPDELS-----FKKGDIIIVLEKSEDGWWKGR-NKGGKE----GLIPS 47

Guanylate kinase;

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  147 YSRPVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLY 223
Cdd:pfam00625   1 SRRPVVLSGPSgvgKSHIKKALLSEYPDKFGYSVPHTTRPPRKGEVDGKDYYFV-SKEEMERDISANEFLEYAQFSGNMY 79

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  224 GTSVQSVREVAEKGKHCILDVSGNAIKRLQLAQLYPIAVFIKPKSVENILEMNKRLMEEQGRKTYDRAMKLEQEFLE-HF 302
Cdd:pfam00625  80 GTSVETIEQIHEQGKIVILDVDPQGVKQLRKAELSPISVFIKPPSLKVLQRRLKGRGKEQEEKINKRMAAAEQEFQHyEF 159

                         170       180
                  ....*....|....*....|...
gi 528482432  303 TAIVQGDTLEEIYNQVKQIIEEQ 325
Cdd:pfam00625 160 DVIIVNDDLEEAYKKLKEALEAE 182

Src Homology 3 domain of Disks large homolog proteins; The DLG-like proteins are scaffolding proteins that cluster at synapses and are also called PSD (postsynaptic density)-95 proteins or SAPs (synapse-associated proteins). They play important roles in synaptic development and plasticity, cell polarity, migration and proliferation. They are members of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. DLG-like proteins contain three PDZ domains and varying N-terminal regions. All DLG proteins exist as alternatively-spliced isoforms. Vertebrates contain four DLG proteins from different genes, called DLG1-4. DLG4 and DLG2 are found predominantly at postsynaptic sites and they mediate surface ion channel and receptor clustering. DLG3 is found axons and some presynaptic terminals. DLG1 interacts with AMPA-type glutamate receptors and is critical in their maturation and delivery to synapses. The SH3 domain of DLG4 binds and clusters the kainate subgroup of glutamate receptors via two proline-rich sequences in their C-terminal tail. It also binds AKAP79/150 (A-kinase anchoring protein). SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 528482432  22 YVRALFDYDITKDSGLPSQGLNFRFGDILHVLNASDEEWWQARHVTTDGEMEEMGVIPSKK 82
Cdd:cd11861    1 YVRALFDYDPSRDSGLPSQGLSFKFGDILHVTNASDDEWWQARRVTPNGEEEEVGVIPSKR 61

Src Homology 3 domain of Disks Large homolog 2; DLG2, also called postsynaptic density-93 (PSD93) or Channel-associated protein of synapse-110 (chapsyn 110), is a scaffolding protein that clusters at synapses and plays an important role in synaptic development and plasticity. The DLG2 delta isoform binds inwardly rectifying potassium Kir2 channels, which determine resting membrane potential in neurons. It regulates the spatial and temporal distribution of Kir2 channels within neuronal membranes. DLG2 is a member of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. DLG2 contains three PDZ domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60        70
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....
gi 528482432  16 SQKRTLYVRALFDYDITKDSGLPSQGLNFRFGDILHVLNASDEEWWQARHVTTDGEMEEMGVIPSKKRVERKER 89
Cdd:cd12032    1 NQKRSLYVRAMFDYEKSKDSGLPSQGLSFRYGDILHVINASDDEWWQARRVTPDGDSEEMGVIPSKRRVERKER 74

guanylate kinase

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 149 RPVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLYGT 225
Cdd:PLN02772 136 KPIVISGPSgvgKGTLISMLMKEFPSMFGFSVSHTTRAPREMEKDGVHYHFT-ERSVMEKEIKDGKFLEFASVHGNLYGT 214

                         90       100       110       120       130       140       150       160
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 226 SVQSVREVAEKGKHCILDVSGNAIKRLQLAQLYPIAVFIKPKSVEnilEMNKRL------MEEQGRKTYDRA-MKLEQ-- 296
Cdd:PLN02772 215 SIEAVEVVTDSGKRCILDIDVQGARSVRASSLEAIFIFICPPSME---ELEKRLrargteTEEQIQKRLRNAeAELEQgk 291

                        170       180
                 ....*....|....*....|....*..
gi 528482432 297 -EFLehFTAIVQGDTLEEIYNQVKQII 322
Cdd:PLN02772 292 sSGI--FDHILYNDNLEECYKNLKKLL 316

Guanosine monophosphate kinase (GMPK, EC 2.7.4.8), also known as guanylate kinase (GKase), catalyzes the reversible phosphoryl transfer from adenosine triphosphate (ATP) to guanosine monophosphate (GMP) to yield adenosine diphosphate (ADP) and guanosine diphosphate (GDP). It plays an essential role in the biosynthesis of guanosine triphosphate (GTP). This enzyme is also important for the activation of some antiviral and anticancer agents, such as acyclovir, ganciclovir, carbovir, and thiopurines.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 150 PVIILGPM---KDRINDDLISEFPDKFGSCVPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLYGTS 226
Cdd:cd00071    1 LIVLSGPSgvgKSTLLKRLLEEFDPNFGFSVSHTTRKPRPGEVDGVDYHFV-SKEEFERLIENGEFLEWAEFHGNYYGTS 79

                         90       100       110       120
                 ....*....|....*....|....*....|....*....|
gi 528482432 227 VQSVREVAEKGKHCILDVSGNAIKRLQLAQLYPIAVFIKP 266
Cdd:cd00071   80 KAAVEEALAEGKIVILEIDVQGARQVKKSYPDAVSIFILP 119

Guanylate kinase [Nucleotide transport and metabolism];

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 177 VPHTTRPKRDYEVDGRDYHFVnSREQMEKDIQDHKFIEAGQYNNHLYGTSVQSVREVAEKGKHCIL--DVSGnAikrLQL 254
Cdd:COG0194   33 VSATTRPPRPGEVDGVDYHFV-SREEFERMIENGEFLEWAEVHGNYYGTPKAEVEEALAAGKDVLLeiDVQG-A---RQV 107

                         90       100       110       120       130       140       150       160
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432 255 AQLYP--IAVFIKPKSVEnilEMNKRLMeeqGRKTYD--------RAMKLEQEFLEHFTAIVQGDTLEEIYNQVKQIIEE 324
Cdd:COG0194  108 KKKFPdaVSIFILPPSLE---ELERRLR---GRGTDSeevierrlAKAREELAHADEFDYVVVNDDLDRAVEELKAIIRA 181

                 .
gi 528482432 325 Q 325
Cdd:COG0194  182 E 182

Src Homology 3 domain of Membrane Protein, Palmitoylated (or MAGUK p55 subfamily member) proteins; The MPP/p55 subfamily of MAGUK (membrane-associated guanylate kinase) proteins includes at least eight vertebrate members (MPP1-7 and CASK), four Drosophila proteins (Stardust, Varicose, CASK and Skiff), and other similar proteins; they all contain one each of the core of three domains characteristic of MAGUK proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, most members except for MPP1 contain N-terminal L27 domains and some also contain a Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. CASK has an additional calmodulin-dependent kinase (CaMK)-like domain at the N-terminus. Members of this subfamily are scaffolding proteins that play important roles in regulating and establishing cell polarity, cell adhesion, and synaptic targeting and transmission, among others. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 528482432  22 YVRALFDYDITKDSGLPSQ--GLNFRFGDILHVLNASDEEWWQARHVTTDGemEEMGVIPSK 81
Cdd:cd11862    1 FVRALFDYDPEEDPLIPCKeaGLSFKKGDILQIVNQDDPNWWQARKVGDPN--GRAGLIPSQ 60

Src Homology 3 domain of Membrane Protein, Palmitoylated 1 (or MAGUK p55 subfamily member 1)-like proteins; This subfamily includes MPP1, CASK (Calcium/calmodulin-dependent Serine protein Kinase), Caenorhabditis elegans lin-2, and similar proteins. MPP1 and CASK are scaffolding proteins from the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). In addition, they also have the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. CASK and lin-2 also contain an N-terminal calmodulin-dependent kinase (CaMK)-like domain and two L27 domains. MPP1 is ubiquitously-expressed and plays roles in regulating neutrophil polarity, cell shape, hair cell development, and neural development and patterning of the retina. CASK is highly expressed in the mammalian nervous system and plays roles in synaptic protein targeting, neural development, and gene expression regulation. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 528482432  22 YVRALFDYDITKDSGLPSQ--GLNFRFGDILHVLNASDEEWWQARHVttDGEMEEMGVIPS 80
Cdd:cd12035    1 YVRAQFDYDPSKDDLIPCQqaGIAFKTGDILQIISKDDHNWWQARKP--GASKEPAGLIPS 59

Src Homology 3 domain of Membrane Protein, Palmitoylated 1 (or MAGUK p55 subfamily member 1); MPP1, also called 55 kDa erythrocyte membrane protein (p55), is a ubiquitously-expressed scaffolding protein that plays roles in regulating neutrophil polarity, cell shape, hair cell development, and neural development and patterning of the retina. It was originally identified as an erythrocyte protein that stabilizes the actin cytoskeleton to the plasma membrane by forming a complex with 4.1R protein and glycophorin C. MPP1 is one of seven vertebrate homologs of the Drosophila Stardust protein, which is required in establishing cell polarity, and it contains the three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, it also contains the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 528482432  22 YVRALFDYDITKDSGLPSQ--GLNFRFGDILHVLNASDEEWWQARhVTTDGEmEEMGVIPS 80
Cdd:cd12080    1 YMRAQFDYDPKKDNLIPCKeaGLKFQTGDIIQIINKDDSNWWQGR-VEGSGE-ESAGLIPS 59

Src Homology 3 domain of Calcium/calmodulin-dependent Serine protein Kinase; CASK is a scaffolding protein that is highly expressed in the mammalian nervous system and plays roles in synaptic protein targeting, neural development, and gene expression regulation. CASK interacts with many different binding partners including parkin, neurexin, syndecans, calcium channel proteins, caskin, among others, to perform specific functions in different subcellular locations. Disruption of the CASK gene in mice results in neonatal lethality while mutations in the human gene have been associated with X-linked mental retardation. Drosophila CASK is associated with both pre- and postsynaptic membranes and is crucial in synaptic transmission and vesicle cycling. CASK contains an N-terminal calmodulin-dependent kinase (CaMK)-like domain, two L27 domains, followed by the core of three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, it also contains the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 528482432  22 YVRALFDYDITKDSGLPSQ--GLNFRFGDILHVLNASDEEWWQARHVTTDGemEEMGVIPS 80
Cdd:cd12081    1 YVRAQFEYDPLKDDLIPCKqaGIRFRVGDILQIISKDDHNWWQAKLENSKN--GTAGLIPS 59

Src Homology 3 domain of Membrane Protein, Palmitoylated 3 (or MAGUK p55 subfamily member 3); MPP3 is a scaffolding protein that colocalizes with MPP5 and CRB1 at the subdpical region adjacent to adherens junctions and may function in photoreceptor polarity. It interacts with some nectins and regulates their trafficking and processing. Nectins are cell-cell adhesion proteins involved in the establishment apical-basal polarity at cell adhesion sites. It is one of seven vertebrate homologs of the Drosophila Stardust protein, which is required in establishing cell polarity, and it contains two L27 domains followed by the core of three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....
gi 528482432  22 YVRALFDYDITKDSGLPSQ--GLNFRFGDILHVLNASDEEWWQARHVttdGEME-EMGVIPSKK 82
Cdd:cd12039    1 FMRALFDYNPYEDRAIPCQeaGLPFKRRDILEVVSQDDPTWWQAKRV---GDTNlRAGLIPSKQ 61

Src homology 3 domain of Src kinase-like Protein Tyrosine Kinases; Src subfamily members include Src, Lck, Hck, Blk, Lyn, Fgr, Fyn, Yrk, Yes, and Brk. Src (or c-Src) proteins are cytoplasmic (or non-receptor) PTKs which are anchored to the plasma membrane. They contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). However, Brk lacks the N-terminal myristoylation sites. Src proteins are involved in signaling pathways that regulate cytokine and growth factor responses, cytoskeleton dynamics, cell proliferation, survival, and differentiation. They were identified as the first proto-oncogene products, and they regulate cell adhesion, invasion, and motility in cancer cells, and tumor vasculature, contributing to cancer progression and metastasis. Src kinases are overexpressed in a variety of human cancers, making them attractive targets for therapy. They are also implicated in acute inflammatory responses and osteoclast function. Src, Fyn, Yes, and Yrk are widely expressed, while Blk, Lck, Hck, Fgr, Lyn, and Brk show a limited expression pattern. This subfamily also includes Drosophila Src42A, Src oncogene at 42A (also known as Dsrc41) which accumulates at sites of cell-cell or cell-matrix adhesion, and participates in Drosphila development and wound healing. It has been shown to promote tube elongation in the tracheal system, is essential for proper cell-cell matching during dorsal closure, and regulates cell-cell contacts in developing Drosophila eyes. The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*....
gi 528482432  23 VRALFDYD-ITKDSglpsqgLNFRFGDILHVLNASDEEWWQARHVTTDGEmeemGVIPS 80
Cdd:cd11845    2 YVALYDYEaRTDDD------LSFKKGDRLQILDDSDGDWWLARHLSTGKE----GYIPS 50

Src homology 3 domains; Src homology 3 (SH3) domains bind to target proteins through sequences containing proline and hydrophobic amino acids. Pro-containing polypeptides may bind to SH3 domains in 2 different binding orientations.

                           10        20        30        40        50
                   ....*....|....*....|....*....|....*....|....*....|....*....
gi 528482432    22 YVRALFDYDITKDsglpsQGLNFRFGDILHVLNASDEEWWQARHVTtdgemEEMGVIPS 80
Cdd:smart00326   4 QVRALYDYTAQDP-----DELSFKKGDIITVLEKSDDGWWKGRLGR-----GKEGLFPS 52

Src homology 3 domain of Fyn and Yrk Protein Tyrosine Kinases; Fyn and Yrk (Yes-related kinase) are members of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. Fyn, together with Lck, plays a critical role in T-cell signal transduction by phosphorylating ITAM (immunoreceptor tyr activation motif) sequences on T-cell receptors, ultimately leading to the proliferation and differentiation of T-cells. In addition, Fyn is involved in the myelination of neurons, and is implicated in Alzheimer's and Parkinson's diseases. Yrk has been detected only in chickens. It is primarily found in neuronal and epithelial cells and in macrophages. It may play a role in inflammation and in response to injury. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 528482432  20 TLYVrALFDYDI-TKDSglpsqgLNFRFGDILHVLNASDEEWWQARHVTTDGEmeemGVIPS 80
Cdd:cd12006    1 TLFV-ALYDYEArTEDD------LSFHKGEKFQILNSSEGDWWEARSLTTGET----GYIPS 51

Src Homology 3 domain superfamily; Src Homology 3 (SH3) domains are protein interaction domains that bind proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. Thus, they are referred to as proline-recognition domains (PRDs). SH3 domains are less selective and show more diverse specificity compared to other PRDs. They have been shown to bind peptide sequences that lack the PxxP motif; examples include the PxxDY motif of Eps8 and the RKxxYxxY sequence in SKAP55. SH3 domain containing proteins play versatile and diverse roles in the cell, including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies, among others. Many members of this superfamily are adaptor proteins that associate with a number of protein partners, facilitating complex formation and signal transduction.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*....
gi 528482432  22 YVRALFDYDitkdsGLPSQGLNFRFGDILHVLNASDEEWWQARHVTtdgemEEMGVIPS 80
Cdd:cd00174    1 YARALYDYE-----AQDDDELSFKKGDIITVLEKDDDGWWEGELNG-----GREGLFPA 49

Src Homology 3 domain of Sdc25/Cdc25 guanine nucleotide exchange factors; This subfamily is composed of the Saccharomyces cerevisiae guanine nucleotide exchange factors (GEFs) Sdc25 and Cdc25, and similar proteins. These GEFs regulate Ras by stimulating the GDP/GTP exchange on Ras. Cdc25 is involved in the Ras/PKA pathway that plays an important role in the regulation of metabolism, stress responses, and proliferation, depending on available nutrients and conditions. Proteins in this subfamily contain an N-terminal SH3 domain as well as REM (Ras exchanger motif) and RasGEF domains at the C-terminus. SH3 domains bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs; they play a role in the regulation of enzymes by intramolecular interactions, changing the subcellular localization of signal pathway components and mediate multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*
gi 528482432  22 YVRALFDYDITKDSGLPsqglnFRFGDILHVLNASDEEWWqarhvttDGEmeemgVIPSKKRVER 86
Cdd:cd11883    1 VVVALYDFTPKSKNQLS-----FKAGDIIYVLNKDPSGWW-------DGV-----IISSSGKVKR 48

C-terminal Src homology 3 domain of Growth factor receptor-bound protein 2 (GRB2) and related proteins; This family includes the adaptor protein GRB2 and related proteins including Drosophila melanogaster Downstream of receptor kinase (DRK), Caenorhabditis elegans Sex muscle abnormal protein 5 (Sem-5), GRB2-related adaptor protein (GRAP), GRAP2, and similar proteins. Family members contain an N-terminal SH3 domain, a central SH2 domain, and a C-terminal SH3 domain. GRB2/Sem-5/DRK is a critical signaling molecule that regulates the Ras pathway by linking tyrosine kinases to the Ras guanine nucleotide releasing protein Sos (son of sevenless), which converts Ras to the active GTP-bound state. GRAP2 plays an important role in T cell receptor (TCR) signaling by promoting the formation of the SLP-76:LAT complex, which couples the TCR to the Ras pathway. GRAP acts as a negative regulator of T cell receptor (TCR)-induced lymphocyte proliferation by downregulating the signaling to the Ras/ERK pathway. The C-terminal SH3 domains (SH3c) of GRB2 and GRAP2 have been shown to bind to classical PxxP motif ligands, as well as to non-classical motifs. GRB2 SH3c binds Gab2 (Grb2-associated binder 2) through epitopes containing RxxK motifs, while the SH3c of GRAP2 binds to the phosphatase-like protein HD-PTP via a RxxxxK motif. SH3 domains are protein interaction domains that typically bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|...
gi 528482432  22 YVRALFDYDITKdsglPSQgLNFRFGDILHVLNASDEEWWQAR 64
Cdd:cd11805    1 RVQALYDFNPQE----PGE-LEFRRGDIITVLDSSDPDWWKGE 38

Src homology 3 domain of the Tight junction proteins, Zonula occludens (ZO) proteins; ZO proteins are scaffolding proteins that associate with each other and with other proteins of the tight junction, zonula adherens, and gap junctions. They play roles in regulating cytoskeletal dynamics at these cell junctions. They are considered members of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. Vertebrates contain three ZO proteins (ZO-1, ZO-2, and ZO-3) with redundant and non-redundant roles. They contain three PDZ domains, followed by SH3 and GuK domains; in addition, ZO-1 and ZO-2 contains a proline-rich (PR) actin binding domain at the C-terminus while ZO-3 contains this PR domain between the second and third PDZ domains. The C-terminal regions of the three ZO proteins are unique. The SH3 domain of ZO-1 has been shown to bind ZONAB, ZAK, afadin, and Galpha12. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*..
gi 528482432  22 YVRALFDYDitkdsGLPSQGLNFRFGDILHVLNASDEE---WWQARHVTTDGEMEEMGVIPSKKRVE 85
Cdd:cd11859    1 YIRTHFDYE-----KPAKGELSFKKGEVFHVVDTLYQGtvgSWQAVRVGRNHQELERGVIPNKSRAE 62

Src homology 3 domain of Yes Protein Tyrosine Kinase; Yes (or c-Yes) is a member of the Src subfamily of proteins, which are cytoplasmic (or non-receptor) PTKs. c-Yes kinase is the cellular homolog of the oncogenic protein (v-Yes) encoded by the Yamaguchi 73 and Esh sarcoma viruses. It displays functional overlap with other Src subfamily members, particularly Src. It also shows some unique functions such as binding to occludins, transmembrane proteins that regulate extracellular interactions in tight junctions. Yes also associates with a number of proteins in different cell types that Src does not interact with, like JAK2 and gp130 in pre-adipocytes, and Pyk2 in treated pulmonary vein endothelial cells. Although the biological function of Yes remains unclear, it appears to have a role in regulating cell-cell interactions and vesicle trafficking in polarized cells. Src kinases contain an N-terminal SH4 domain with a myristoylation site, followed by SH3 and SH2 domains, a tyr kinase domain, and a regulatory C-terminal region containing a conserved tyr. They are activated by autophosphorylation at the tyr kinase domain, but are negatively regulated by phosphorylation at the C-terminal tyr by Csk (C-terminal Src Kinase). The SH3 domain of Src kinases contributes to substrate recruitment by binding adaptor proteins/substrates, and regulation of kinase activity through an intramolecular interaction. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|.
gi 528482432  20 TLYVrALFDYDitkdsGLPSQGLNFRFGDILHVLNASDEEWWQARHVTTDgemeEMGVIPS 80
Cdd:cd12007    1 TIFV-ALYDYE-----ARTTEDLSFKKGERFQIINNTEGDWWEARSIATG----KNGYIPS 51

Src homology 3 domain of Signal Transducing Adaptor Molecule 2; STAM2, also called EAST (Epidermal growth factor receptor-associated protein with SH3 and TAM domain) or Hbp (Hrs binding protein), is part of the endosomal sorting complex required for transport (ESCRT-0). It plays a role in sorting mono-ubiquinated endosomal cargo for trafficking to the lysosome for degradation. It is also involved in the regulation of exocytosis. STAMs were discovered as proteins that are highly phosphorylated following cytokine and growth factor stimulation. They function in cytokine signaling and surface receptor degradation, as well as regulate Golgi morphology. They associate with many proteins including Jak2 and Jak3 tyrosine kinases, Hrs, AMSH, and UBPY. STAM adaptor proteins contain VHS (Vps27, Hrs, STAM homology), ubiquitin interacting (UIM), and SH3 domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|...
gi 528482432  23 VRALFDYDITKDSGLpsqglNFRFGDILHVLNASDEEWWQARH 65
Cdd:cd11963    4 VRALYDFEAVEDNEL-----TFKHGEIIIVLDDSDANWWKGEN 41

Src Homology 3 domain of Voltage-dependent L-type calcium channel subunit beta; Voltage-dependent calcium channels (Ca(V)s) are multi-protein complexes that regulate the entry of calcium into cells. They impact muscle contraction, neuronal migration, hormone and neurotransmitter release, and the activation of calcium-dependent signaling pathways. They are composed of four subunits: alpha1, alpha2delta, beta, and gamma. The beta subunit is a soluble and intracellular protein that interacts with the transmembrane alpha1 subunit. It facilitates the trafficking and proper localization of the alpha1 subunit to the cellular plasma membrane. Vertebrates contain four different beta subunits from distinct genes (beta1-4); each exists as multiple splice variants. All are expressed in the brain while other tissues show more specific expression patterns. The beta subunits show similarity to MAGUK (membrane-associated guanylate kinase) proteins in that they contain SH3 and inactive guanylate kinase (GuK) domains; however, they do not appear to contain a PDZ domain. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  23 VRALFDYDITKDSGLPSQGLNFRFG--DILHVLNASDEEWWQARHVttdGEMEEMGVIPS 80
Cdd:cd11863    3 VRTNVGYDGSLDDDSPVPGYAVSFEakDFLHIKEKYNNDWWIGRLV---KEGCDIGFIPS 59

Src homology 3 domain of APC-Stimulated guanine nucleotide Exchange Factor 2; ASEF2, also called Spermatogenesis-associated protein 13 (SPATA13), is a GEF that localizes with actin at the leading edge of cells and is important in cell migration and adhesion dynamics. GEFs activate small GTPases by exchanging bound GDP for free GTP. ASEF2 can activate both Rac 1 and Cdc42, but only Rac1 activation is necessary for increased cell migration and adhesion turnover. Together with APC (adenomatous polyposis coli) and Neurabin2, a scaffold protein that binds F-actin, it is involved in regulating HGF-induced cell migration. ASEF2 contains a SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40
                 ....*....|....*....|....*....|....*....|....
gi 528482432  21 LYVRALFDYdITKDSglpsQGLNFRFGDILHVLNASDEEWWQAR 64
Cdd:cd11974    1 VYAEALWDH-VTMDD----QELAFKAGDVIRVLEASNKDWWWGR 39

Src homology 3 domain of Disks Large homolog 5; DLG5 is a multifunctional scaffold protein that is located at sites of cell-cell contact and is involved in the maintenance of cell shape and polarity. Mutations in the DLG5 gene are associated with Crohn's disease (CD) and inflammatory bowel disease (IBD). DLG5 is a member of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. DLG5 contains 4 PDZ domains as well as an N-terminal domain of unknown function. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60        70
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gi 528482432  22 YVRALFDYditkdSGLPSQGLNFRFGDILHV----LNASDEEW--WQARHvttDGEMEEMGVIPSKKRVE 85
Cdd:cd11860    1 YVRALFDR-----SAENEDELSFKKDDILYVdntmFNGVFGQWraWLVDE---EGRKRKCGIIPSKYKVE 62

Src homology 3 domain of APC-Stimulated guanine nucleotide Exchange Factor; ASEF, also called ARHGEF4, exists in an autoinhibited form and is activated upon binding of the tumor suppressor APC (adenomatous polyposis coli). GEFs activate small GTPases by exchanging bound GDP for free GTP. ASEF can activate Rac1 or Cdc42. Truncated ASEF, which is found in colorectal cancers, is constitutively active and has been shown to promote angiogenesis and cancer cell migration. ASEF contains a SH3 domain followed by RhoGEF (also called Dbl-homologous or DH) and Pleckstrin Homology (PH) domains. In its autoinhibited form, the SH3 domain of ASEF forms an extensive interface with the DH and PH domains, blocking the Rac binding site. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*
gi 528482432  16 SQKRTLYVRALFDYdITKDSglpsQGLNFRFGDILHVLNASDEEWWQARHVTTDG 70
Cdd:cd11973   13 SDGSVVCAEALWDH-VTMDD----QELGFKAGDVIEVMDATNKEWWWGRVLDSEG 62

First Src Homology 3 domain of the fungal endocytic adaptor protein Sla1p; Sla1p facilitates endocytosis by playing a role as an adaptor protein in coupling components of the actin cytoskeleton to the endocytic machinery. It interacts with Abp1p, Las17p and Pan1p, which are activator proteins of actin-related protein 2/3 (Arp2/3). Sla1p contains multiple domains including three SH3 domains, a SAM (sterile alpha motif) domain, and a Sla1 homology domain 1 (SHD1), which binds to the NPFXD motif that is found in many integral membrane proteins such as the Golgi-localized Arf-binding protein Lsb5p and the P4-ATPases, Drs2p and Dnf1p. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|..
gi 528482432  23 VRALFDYDitkdsglpSQG---LNFRFGDILHVLNASDEEWWQAR-HVTTDGEMEEMGVIPS 80
Cdd:cd11773    2 YKALYDYE--------PQTedeLTIQEDDILYLLEKSDDDWWKVKlKVNSSDDDEPVGLVPA 55

Src homology 3 domain of High osmolarity signaling protein Sho1p; Sho1p (or Sho1), also called SSU81 (Suppressor of SUA8-1 mutation), is a yeast membrane protein that regulates adaptation to high salt conditions by activating the HOG (high-osmolarity glycerol) pathway. High salt concentrations lead to the localization to the membrane of the MAPKK Pbs2, which is then activated by the MAPKK Ste11 and in turn, activates the MAPK Hog1. Pbs2 is localized to the membrane though the interaction of its PxxP motif with the SH3 domain of Sho1p. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|
gi 528482432  23 VRALFDYDITKDSglPSQgLNFRFGDILHVlnaSDEE--WWQARHvtTDGemeEMGVIPS 80
Cdd:cd11855    2 ARALYPYDASPDD--PNE-LSFEKGEILEV---SDTSgkWWQARK--SNG---ETGICPS 50

Src homology 3 domain of RUN and SH3 domain-containing protein 1; RUSC1, also called NESCA (New molecule containing SH3 at the carboxy-terminus), is highly expressed in the brain and is translocated to the nuclear membrane from the cytoplasm upon stimulation with neurotrophin. It plays a role in facilitating neurotrophin-dependent neurite outgrowth. It also interacts with NEMO (or IKKgamma) and may function in NEMO-mediated activation of NF-kB. RUSC proteins are adaptor proteins consisting of RUN, leucine zipper, and SH3 domains. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*..
gi 528482432  23 VRALFDYDITKDsglpsqGLNFRFGDILHVLNASDEEWWQARHvttdGEMEemGVIP 79
Cdd:cd11958    2 VRALCDHAGSES------QLSFRKGEELQVLGTVDEDWIRCRR----GDRE--GLVP 46

Src Homology 3 domain of Tec-like Protein Tyrosine Kinases; The Tec (Tyrosine kinase expressed in hepatocellular carcinoma) subfamily is composed of Tec, Btk, Bmx (Etk), Itk (Tsk, Emt), Rlk (Txk), and similar proteins. They are cytoplasmic (or nonreceptor) tyr kinases containing Src homology protein interaction domains (SH3, SH2) N-terminal to the catalytic tyr kinase domain. Most Tec subfamily members (except Rlk) also contain an N-terminal pleckstrin homology (PH) domain, which binds the products of PI3K and allows membrane recruitment and activation. In addition, some members contain the Tec homology (TH) domain, which contains proline-rich and zinc-binding regions. Tec kinases are expressed mainly by haematopoietic cells, although Tec and Bmx are also found in endothelial cells. B-cells express Btk and Tec, while T-cells express Itk, Txk, and Tec. Collectively, Tec kinases are expressed in a variety of myeloid cells such as mast cells, platelets, macrophages, and dendritic cells. Each Tec kinase shows a distinct cell-type pattern of expression. The function of Tec kinases in lymphoid cells have been studied extensively. They play important roles in the development, differentiation, maturation, regulation, survival, and function of B-cells and T-cells. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies.

                         10        20        30        40        50
                 ....*....|....*....|....*....|....*....|....*....|....*...
gi 528482432  23 VRALFDYDITKDSGLPsqglnFRFGDILHVLNASDEEWWQARhvttDGEMEEmGVIPS 80
Cdd:cd11768    2 VVALYDFQPIEPGDLP-----LEKGEEYVVLDDSNEHWWRAR----DKNGNE-GYIPS 49