Glyceride-cysteine lipoproteins and secretion by Gram-positive bacteria

The membrane penicillinases of Bacillus licheniformis and Bacillus cereus are lipoproteins with N-terminal glyceride thioether modification identical to that of the Escherichia coli outer membrane lipoprotein. They are readily labeled with [3H]palmitate present during exponential growth. At the same time, a few other proteins in each organism become labeled and can be detected by fluorography after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total membrane proteins. We distinguish these proteins from the O-acyl proteolipids by demonstrating the formation of glyceryl cysteine sulfone after performic acid oxidation and hydrolysis of the protein. By this criterion, B. licheniformis and B. cereus contain sets of lipoproteins larger in average molecular weight than that of E. coli. Members of the sets probably are under a variety of physiological controls, as indicated by widely differing relative labeling intensity in different media. The set in B. licheniformis shares with membrane penicillinase a sensitivity to release from protoplasts by mild trypsin treatment, which suggests similar orientation on the outside of the membrane. At least one protein is the membrane-bound partner of an extracellular hydrophilic protein, the pair being related as membrane and exopenicillinases are. We propose that the lipoproteins of gram-positive organisms are the functional equivalent of periplasmic proteins in E. coli and other gram-negative bacteria, prevented from release by anchorage to the membrane rather than by a selectively impermeable outer membrane.