Src homology 2 domain found in Signal-transducing adaptor protein (STAP) family
STAP1 and STAP2 are signal-transducing adaptor proteins. They are composed of a Pleckstrin homology (PH) and SH2 domains along with several tyrosine phosphorylation sites. STAP-1 is an ortholog of BRDG1 (BCR downstream signaling 1). STAP1 protein functions as a docking protein acting downstream of Tec tyrosine kinase in B cell antigen receptor signaling. The protein is phosphorylated by Tec and participates in a positive feedback loop, increasing Tec activity. STAP1 has been shown to interact with C19orf2, an unconventional prefoldin RPB5 interactor. The STAP2 protein is the substrate of breast tumor kinase, an Src-type non-receptor tyrosine kinase that mediates the interactions linking proteins involved in signal transduction pathways. STAP2 has alternative splicing variants. STAP2 has been shown to interact with tyrosine-protein kinase 6 (PTK6). In general SH2 domains are involved in signal transduction. They typically bind pTyr-containing ligands via two surface pockets, a pTyr and hydrophobic binding pocket, allowing proteins with SH2 domains to localize to tyrosine phosphorylated sites.
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