Phosphatase Subfamily PPIP5K
PPIP5K is a phosphoinositol kinase that also has a pseudophosphatase domain which binds to PtdIns(3,4,5)P3. PPIP5K converts InsP6 and 5-InsP7 to 1-InsP7 and InsP8.
PPIP5K is found in most eukaryotes, but is missing in alveolates. Most vertebrates have at least two copies, while invertebrates usually have one.
Unlike other HP2 subfamilies which are protein or non-protein phosphatases, the HP2 domain of PPIP5K is not catalytically active. Instead, it binds PtdIns(3,4,5)P3, in part using an inserted partial PH (pleckstrin homology) domain . The HP2 domains of PPIP5Ks are longer than those of other HP2 subfamilies, due to insertions at multiple sites.
Catalytic activity and functions
The phosphatase domains of human PPIP5K1 and PPIP5K2 are catalytically inactive, though they bear the histidine residue at catalytic core (figure 5 in ). It is unclear whether PPIP5K are inactive in other genomes.
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