Catalytic inositol polyphosphate 5-phosphatase (INPP5c) domain of Saccharomyces cerevisiae Inp51p, Inp52p, and Inp53p, and related proteins
This subfamily contains the INPP5c domain of three Saccharomyces cerevisiae synaptojanin-like inositol polyphosphate 5-phosphatases (INP51, INP52, and INP53), Schizosaccharomyces pombe synaptojanin (SPsynaptojanin), and related proteins. It belongs to a family of Mg2+-dependent inositol polyphosphate 5-phosphatases, which hydrolyze the 5-phosphate from the inositol ring of various 5-position phosphorylated phosphoinositides (PIs) and inositol phosphates (IPs), and to the large EEP (exonuclease/endonuclease/phosphatase) superfamily that contains functionally diverse enzymes that share a common catalytic mechanism of cleaving phosphodiester bonds. In addition to this INPP5c domain, these proteins have an N-terminal catalytic Sac1-like domain (found in other proteins including the phophoinositide phosphatase Sac1p), and a C-terminal proline-rich domain (PRD). The Sac1 domain allows Inp52p and Inp53p to recognize and dephosphorylate a wider range of substrates including PI3P, PI4P, and PI(3,5)P2. The Sac1 domain of Inp51p is non-functional. Disruption of any two of INP51, INP52, and INP53, in S. cerevisiae leads to abnormal vacuolar and plasma membrane morphology. During hyperosmotic stress, Inp52p and Inp53p localize at actin patches, where they may facilitate the hydrolysis of PI(4,5)P2, and consequently promote actin rearrangement to regulate cell growth. SPsynaptojanin is also active against a range of soluble and lipid inositol phosphates, including I(1,4,5)P3, I(1,3,4,5)P4, I(1,4,5,6)P4, PI(4,5)P2, and PIP3. Transformation of S. cerevisiae with a plasmid expressing the SPsynaptojanin 5-phosphatase domain rescues inp51/inp52/inp53 triple-mutant strains.
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