CRYSTAL-STRUCTURE OF THE PHOSPHATIDYLINOSITOL-SPECIFIC PHOSPHOLIPASE-C FROM BACILLUS-CEREUS IN COMPLEX WITH MYOINOSITOL

Phosphatidylinositol (PI), once regarded as an obscure component of me mbranes, is now recognized as an important reservoir of second messeng er precursors and as an anchor for membrane enzymes. PI-specifiE phosp holipase C (PI-PLC) is the enzyme that cleaves PI, invoking numerous c ellular responses. The crystal structure of PI-PLC from Bacillus cereu s (EC 3.1.4.10) has been solved at 2.6 Angstrom resolution and refined to a crystallographic R factor of 18.7%. The structure consists of an imperfect (beta alpha)(8)-barrel similar to that first observed for t riose phosphate isomerase and does not resemble any other known phosph olipase structure. The active site of the enzyme has been identified b y determining the structure of PI-PLC in complex with its inhibitor, m yo-inositol, at 2.6; Angstrom resolution (R factor = 19.5%). This subs trate-like inhibitor interacts with a number of residues highly conser ved among prokaryotic PI-PLCs. Residues His32 and His82, which are als o conserved between prokaryotic and eukaryotic PI-PLCs, most likely ac t as general base and acid respectively in a catalytic mechanism analo gous to that observed for ribonucleases.