Src homology 3 domain of Obscurin and similar proteins
Obscurin is a giant muscle protein that is concentrated at the peripheries of Z-disks and M-lines. It binds small ankyrin I, a component of the sarcoplasmic reticulum (SR) membrane. It is associated with the contractile apparatus through binding with titin and sarcomeric myosin. It plays important roles in the organization and assembly of the myofibril and the SR. Obscurin has been observed as alternatively-spliced isoforms. The major isoform in sleletal muscle, approximately 800 kDa in size, is composed of many adhesion modules and signaling domains. It harbors 49 Ig and 2 FNIII repeats at the N-terminues, a complex middle region with additional Ig domains, an IQ motif, and a conserved SH3 domain near RhoGEF and PH domains, and a non-modular C-terminus with phosphorylation motifs. The obscurin gene also encodes two kinase domains, which are not part of the 800 kDa form of the protein, but is part of smaller spliced products that present in heart muscle. 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.
Jiyao W et al.(2023). "The conserved domain database in 2023.",