The protein deficient in Lowe syndrome is a phosphatidylinositol-4,5-bisphosphate 5-phosphatase.

Lowe syndrome, also known as oculocerebrorenal syndrome, is caused by mutations in the X chromosome-encoded OCRL gene.
The OCRL protein is 51% identical to inositol polyphosphate 5-phosphatase II (5-phosphatase II) from human platelets over a span of 744 aa, suggesting that OCRL may be a similar enzyme.
We engineered a construct of the OCRL cDNA that encodes amino acids homologous to the platelet 5-phosphatase for expression in baculovirus-infected Sf9 insect cells.
This cDNA encodes aa 264-968 of the OCRL protein.
The recombinant protein was found to catalyze the reactions also carried out by platelet 5-phosphatase II. Thus OCRL converts inositol 1, 4, 5-trisphosphate to inositol 1, 4-bisphosphate, and it converts inositol 1, 3, 4, 5-tetrakisphosphate to inositol 1, 3, 4-trisphosphate.
Most important, the enzyme converts phosphatidylinositol 4, 5-bisphosphate to phosphatidylinositol 4-phosphate.
The relative ability of OCRL to catalyze the three reactions is different from that of 5-phosphatase II and from that of another 5-phosphatase isoenzyme from platelets, 5-phosphatase I. The recombinant OCRL protein hydrolyzes the phospholipid substrate 10- to 30-fold better than 5-phosphatase II, and 5-phosphatase I does not cleave the lipid at all.
We also show that OCRL functions as a phosphatidylinositol 4, 5-bisphosphate 5-phosphatase in OCRL-expressing Sf9 cells.
These results suggest that OCRL is mainly a lipid phosphatase that may control cellular levels of a critical metabolite, phosphatidylinositol 4, 5-bisphosphate.
Deficiency of this enzyme apparently causes the protean manifestations of Lowe syndrome.. 
