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Inter-Src homology 2 (iSH2) helical domain of Class IA Phosphoinositide 3-kinase Regulatory subunit 1, PIK3R1, also called p85alpha PI3Ks catalyze the transfer of the gamma-phosphoryl group from ATP to the 3-hydroxyl of the inositol ring of D-myo-phosphatidylinositol (PtdIns) or its derivatives. They play an important role in a variety of fundamental cellular processes, including cell motility, the Ras pathway, vesicle trafficking and secretion, immune cell activation and apoptosis. They are classified according to their substrate specificity, regulation, and domain structure. Class IA PI3Ks are heterodimers of a p110 catalytic (C) subunit and a p85-related regulatory (R) subunit. The R subunit down-regulates PI3K basal activity, stabilizes the C subunit, and plays a role in the activation downstream of tyrosine kinases. All R subunits contain two SH2 domains that flank an intervening helical domain (iSH2), which binds to the N-terminal adaptor-binding domain (ABD) of the catalytic subunit. In addition, p85alpha, also called PIK3R1, contains N-terminal SH3 and GAP domains. p85alpha carry functions independent of its PI3K regulatory role. It can independently stimulate signaling pathways involved in cytoskeletal rearrangements. Insulin-sensitive tissues express splice variants of the PIK3R1 gene, p50alpha and p55alpha, which may play important roles in insulin signaling during lipid and glucose metabolism. Mice deficient with PIK3R1 die perinatally, indicating its importance in development. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",