FYVE domain found in metazoan PIKfyve, fungal and plant Fab1, and similar proteins
PIKfyve, also termed FYVE finger-containing phosphoinositide kinase, or 1-phosphatidylinositol 3-phosphate 5-kinase, or phosphatidylinositol 3-phosphate 5-kinase (PIP5K3), or phosphatidylinositol 3-phosphate 5-kinase type III (PIPkin-III or type III PIP kinase), is a phosphoinositide 5-kinase that forms a complex with its regulators, the scaffolding protein Vac14 and the lipid phosphatase Fig4. The complex is responsible for synthesizing phosphatidylinositol 3,5-bisphosphate [PtdIns(3,5)P2] from phosphatidylinositol 3-phosphate (PtdIns3P or PI3P). Then phosphatidylinositol-5-phosphate (PtdIns5P) is generated directly from PtdIns(3,5)P2. PtdIns(3,5)P2 and PtdIns5P regulate endosomal trafficking and responses to extracellular stimuli. At this point, PIKfyve is vital in early embryonic development. Moreover, PIKfyve forms a complex with ArPIKfyve (associated regulator of PIKfyve) and SAC3 at the endomembranes, which plays a role in receptor tyrosine kinase (RTK) degradation. The phosphorylation of PIKfyve by AKT can facilitate Epidermal growth factor receptor (EGFR) degradation. In addition, PIKfyve may participate in the regulation of the glutamate transporters EAAT2, EAAT3 and EAAT4, and the cystic fibrosis transmembrane conductance regulator (CFTR). It is also essential for systemic glucose homeostasis and insulin-regulated glucose uptake/GLUT4 translocation in skeletal muscle. It can be activated by protein kinase B (PKB/Akt) and further up-regulates human ether-a-go-go (hERG) channels. This family also includes the yeast and plant orthologs of human PIKfyve, Fab1. PIKfyve and its orthologs share a similar architecture. They contain an N-terminal FYVE domain, a middle region related to the CCT/TCP-1/Cpn60 chaperonins that are involved in productive folding of actin and tubulin, a second middle domain that contains a number of conserved cysteine residues (CCR) unique to this family, and a C-terminal lipid kinase domain related to PtdInsP kinases.
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