Fluorescent phosphatidylinositol 4,5-bisphosphate derivatives with modified 6-hydroxy group as novel substrates for phospholipase C

The capacity to monitor spatiotemporal activity of phospholipase C (PLC) isozymes with a PLC-selective sensor would dramatically enhance understanding of the physiological function and disease relevance of these signaling proteins. Previous structural and biochemical studies defined critical roles for several of the functional groups of the endogenous substrate of PLC isozymes, phosphatidylinositol 4,5-bisphosphate (PIP(2)), indicating that these sites cannot be readily modified without compromising interactions with the lipase active site. However, the role of the 6-hydroxy group of PIP(2) for interaction and hydrolysis by PLC has not been explored, possibly due to challenges in synthesizing 6-hydroxy derivatives. Here, we describe an efficient route for the synthesis of novel, fluorescent PIP(2) derivatives modified at the 6-hydroxy group. Two of these derivatives were used in assays of PLC activity in which the fluorescent PIP(2) substrates were separated from their diacylglycerol products and reaction rates quantified by fluorescence. Both PIP(2) analogues effectively function as substrates of PLC-δ1, and the K(M) and V(max) values obtained with one of these are similar to those observed with native PIP(2) substrate. These results indicate that the 6-hydroxy group can be modified to develop functional substrates for PLC isozymes, thereby serving as the foundation for further development of PLC-selective sensors.