Phosphatidylcholine-preferring phospholipase C from B. cereus. Function, structure, and mechanism

The PLC class of enzymes has been studied extensively over the past 15-20 y ears because of their involvement in signaling pathways in which extracellu lar messages are delivered to the cell to induce a response. Of the PLC iso enzymes, the PI-PLCs have perhaps been examined in the greatest detail beca use of their key role in initiating cellular response by hydrolyzing the ph osphodiester bond of phosphatidylinositols and their phosphorylated derivat ives to release the second messengers IP3 and DAG. However, the extended re lease of DAG that is critical to maintaining the stimulatory response arise s from hydrolysis of the more abundant phosphatidylcholine by PC-PLC or by PLD followed by phosphatidic acid phosphatase. Because no eukaryotic PC-PLC has been cloned or isolated in pure form, the phosphatidylcholine-preferri ng PLC from B. cereus (PLCBc) has emerged as a focal point for investigatio n and as a putative model for mammalian PC-PLCs. The similarity of the acti ve site of PLCBc with other phosphoryl transfer enzymes has also served as a stimulus for mechanistic studies. The present account details recent stud ies of this important member of the PLC superfamily of enzymes.