SH3 domain

The SRC Homology 3 Domain (or SH3 domain) is a small protein domain of about 60 amino acids residues first identified as a conserved sequence in the viral adaptor protein v-Crk and the non-catalytic parts of enzymes such as phospholipase and several cytoplasmic tyrosine kinases such as Abl and Src. It has also been identified in several other protein families such as: PI3 Kinase, Ras GTPase-activating protein, CDC24 and cdc25. SH3 domains are found in proteins of signaling pathways regulating the cytoskeleton, the Ras protein, and the Src kinase and many others. They also regulate the activity state of adaptor proteins and other tyrosine kinases and are thought to increase the substrate specificity of some tyrosine kinases by binding far away from the active site of the kinase. Approximately 300 SH3 domains are found in proteins encoded in the human genome.