Interaction with phospholipids of a membrane thiol peptidase that is essential for the signal transduction of mating pheromone in Rhodosporidium toruloides.

Interaction with phospholipids of a membrane thiol peptidase [referred to as trigger peptidase (TPase), T. Miyakawa et al. (1987) J. Bacteriol. 169, 1626-1631] that plays a key role in the signalling of a lipopeptidyl mating pheromone at the cell surface of pheromone-target cell (mating type a) of Rhodosporidium toruloides was studied. The activity of highly purified TPase which requires phospholipids was restored by reconstitution of the enzyme into liposomes prepared with phospholipids extracted from the yeast cell. The presence of Ca2+ was essential for both the reconstitution process and the catalytic reaction of TPase. Triton X-100 mixed micelles containing phospholipids also activated the enzyme. The specificity and stoichiometry of activation by phospholipids was investigated by determination of TPase in the presence of mixed micelles that contained defined classes and numbers of phospholipid molecules in the Triton X-100 micelles. It was demonstrated that TPase is activated by mixed micelles containing 2-6 molecules of phosphatidylserine or phosphatidylethanolamine. Other phospholipids of the membranes of this organism, such as phosphatidylcholine and phosphatidylglycerol, had little effect on activation, indicating that the amino group of the phospholipids may be required for the function of TPase. Direct evidence for the interaction of TPase and Triton X-100/phosphatidylserine mixed micelles was obtained by molecular sieve chromatography on Sephacryl S-200. These data established that a phospholipid bilayer is not a requirement for TPase activation, and that the purified enzyme can be activated by a relatively small number of phospholipid molecules of specific classes.