C2 domain present in class I alpha phosphatidylinositol 3-kinases (PI3Ks)
PI3Ks (AKA phosphatidylinositol (PtdIns) 3-kinases) regulate cell processes such as cell growth, differentiation, proliferation, and motility. PI3Ks work on phosphorylation of phosphatidylinositol, phosphatidylinositide (4)P (PtdIns (4)P),2 or PtdIns(4,5)P2. Specifically they phosphorylate the D3 hydroxyl group of phosphoinositol lipids on the inositol ring. There are 3 classes of PI3Ks based on structure, regulation, and specificity. All classes contain a C2 domain, a PIK domain, and a kinase catalytic domain. The members here are class I, alpha isoform PI3Ks and contain both a Ras-binding domain and a p85-binding domain. Class II PI3Ks contain both of these as well as a PX domain, and a C-terminal C2 domain containing a nuclear localization signal. C2 domains fold into an 8-standed beta-sandwich that can adopt 2 structural arrangements: Type I and Type II, distinguished by a circular permutation involving their N- and C-terminal beta strands. Many C2 domains are Ca2+-dependent membrane-targeting modules that bind a wide variety of substances including bind phospholipids, inositol polyphosphates, and intracellular proteins. Most C2 domain proteins are either signal transduction enzymes that contain a single C2 domain, such as protein kinase C, or membrane trafficking proteins which contain at least two C2 domains, such as synaptotagmin 1. However, there are a few exceptions to this including RIM isoforms and some splice variants of piccolo/aczonin and intersectin which only have a single C2 domain. C2 domains with a calcium binding region have negatively charged residues, primarily aspartates, that serve as ligands for calcium ions. Members have a type-I topology.