PI3Kc

Phosphoinositide 3-kinase, catalytic domain
PI3Kc
SMART accession number:SM00146
Description: Phosphoinositide 3-kinase isoforms participate in a variety of processes, including cell motility, the Ras pathway, vesicle trafficking and secretion, and apoptosis. These homologues may be either lipid kinases and/or protein kinases: the former phosphorylate the 3-position in the inositol ring of inositol phospholipids. The ataxia telangiectesia-mutated gene produced, the targets of rapamycin (TOR) and the DNA-dependent kinase have not been found to possess lipid kinase activity. Some of this family possess PI-4 kinase activities.
Interpro abstract (IPR000403):

Phosphatidylinositol 3-kinase (PI3-kinase) (EC 2.7.1.137) [(PUBMED:1322797)] is an enzyme that phosphorylates phosphoinositides on the 3-hydroxyl group of the inositol ring. The three products of PI3-kinase - PI-3-P, PI-3,4-P(2) and PI-3,4,5-P(3) function as secondary messengers in cell signalling. Phosphatidylinositol 4-kinase (PI4-kinase) (EC 2.7.1.67) [(PUBMED:8194527)] is an enzyme that acts on phosphatidylinositol (PI) in the first committed step in the production of the secondary messenger inositol-1'4'5'-trisphosphate. This domain is also present in a wide range of protein kinases, involved in diverse cellular functions, such as control of cell growth, regulation of cell cycle progression, a DNA damage checkpoint, recombination, and maintenance of telomere length. Despite significant homology to lipid kinases, no lipid kinase activity has been demonstrated for any of the PIK-related kinases [(PUBMED:12456783)].

The PI3- and PI4-kinases share a well conserved domain at their C-terminal section; this domain seems to be distantly related to the catalytic domain of protein kinases [(PUBMED:8387896), (PUBMED:12151228)]. The catalytic domain of PI3K has the typical bilobal structure that is seen in other ATP-dependent kinases, with a small N-terminal lobe and a large C-terminal lobe. The core of this domain is the most conserved region of the PI3Ks. The ATP cofactor binds in the crevice formed by the N-and C-terminal lobes, a loop between two strands provides a hydrophobic pocket for binding of the adenine moiety, and a lysine residue interacts with the alpha-phosphate. In contrast to protein kinases, the PI3K loop which interacts with the phosphates of the ATP and is known as the glycine-rich or P-loop, contains no glycine residues. Instead, contact with the ATP -phosphate is maintained through the side chain of a conserved serine residue.

GO function:phosphotransferase activity, alcohol group as acceptor (GO:0016773)
Family alignment:
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There are 5459 PI3Kc domains in 5458 proteins in SMART's nrdb database.

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