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Src Homology 3 domain of Mixed Lineage Kinases MLKs are Serine/Threonine Kinases (STKs), catalyzing the transfer of the gamma-phosphoryl group from ATP to S/T residues on protein substrates. MLKs act as mitogen-activated protein kinase kinase kinases (MAP3Ks, MKKKs, MAPKKKs), which phosphorylate and activate MAPK kinases (MAPKKs or MKKs or MAP2Ks), which in turn phosphorylate and activate MAPKs during signaling cascades that are important in mediating cellular responses to extracellular signals. MLKs play roles in immunity and inflammation, as well as in cell death, proliferation, and cell cycle regulation. Mammals have four MLKs (MLK1-4), mostly conserved in vertebrates, which contain an SH3 domain, a catalytic kinase domain, a leucine zipper, a proline-rich region, and a CRIB domain that mediates binding to GTP-bound Cdc42 and Rac. 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.",