Phosphatidylinositol-specific phosphatase

The classical PTPs can be subdivided into receptorlike PTPs and nonreceptor, cytosolic PTPs. The second category of PTPs are broadly defined as dual specificity phosphatases (DSPs), which dephosphorylate pSer/ pThr as well as pTyr. MAP kinase phosphatases (MKPs) ( MAP kinase cascades) and PTEN are examples of DSP family members. Remarkably, PTEN also has lipid phosphatase activity that is specific for phosphatidylinositol-3,4,5-trisphosphate generated in response to the actions of PI3K. Finally, the class of low molecular mass (LM-) PTPs and that of CDC25 PTPs accomplish the cells repertoire of PTPs (Fig. 3). 

Schaletzky, J, Dove, SK, Short, B, Lorenzo, O, Clague, MJ and Barr, FA (2003) Phosphatidylinositol-5-phosphate activation and conserved substrate specificity of the myotubularin phosphatidylinositol 3-phosphatases. Curr Biol, 13, 504-509. 

The preparation of a photoaffinity probe possessing biotinyl and azidobenzoyl moieties of Ins(l,4,5)P3 has been described which has similar biological function and potency to IP3 with respect to inhibition of [ H]IP3-5-phosphatase as well as the ability to photolyse at the IP3 recognizing domain of the protein. The synthesis of the myoinositol derivative (84) as a fluorescent substrate for assaying phosphatidylinositol-specific PLC has been reported. ... 

Recent studies have suggested that certain plasma membrane-bound siali-dases are linked to the membranes via a GPI anchor, as observed with the sialidase from T. cruzi (Rosenberg et al., 1991). Phosphatidylinositol-specific phospholipase C (PIPLC) released sialidase activity (28% of total) from purified synaptosomal membranes of pig brain, but not from lysosomal membranes (Chiarini et al., 1990). The presence of GPI-anchored sialidase was also shown in human erythrocyte membranes (Chiarini et al., 1993). On the other hand, the sialidase activity in rat brain myelin could not be solubilized with PIPLC despite a concomitant release of alkaline phosphatase activity (about 40% of total), suggesting a different mode of association of the enzyme with the membranes (Saito and Yu, unpublished data). 

The evidence that phosphatidylinositol has a role in protein anchoring comes from two sources (a) the release of certain membrane proteins following digestion with a phosphatidylinositol-specific phospholipase C and (b) analysis of the anchoring domain of some of these membrane proteins. Examples of proteins believed to be attached thus to membranes include alkaline phosphatase, acetylcholinesterase, 5 -nucleotidase and the variant surface glycoprotein (VSG) from Trypanosoma brucei, (The latter is responsible for the ability of this parasitic protozoan to evade the victim s immune defence system and so cause sleeping sickness.)... 

R. Micanovic, L. D. Gerber, J. Berger, K. Kodukula S. Udenfriend. Selectivity of the cleavage/attachment site of phosphatidylinositol-glycan-anchored membrane proteins determined by site-specific mutagenesis at Asp-484 of placental alkaline phosphatase. Proc Natl Acad Sci USA, 1990, 87, 157-161. 

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