C2 domain second repeat present in class II phosphatidylinositol 3-kinases (PI3Ks)
There are 3 classes of PI3Ks based on structure, regulation, and specificity. All classes contain a N-terminal C2 domain, a PIK domain, and a kinase catalytic domain. Unlike class I and class III, class II PI3Ks have additionally a PX domain and a C-terminal C2 domain containing a nuclear localization signal both of which bind phospholipids though in a slightly different fashion. 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. 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. This cd contains the second C2 repeat, C2B, and has a type-I topology.
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