The role of lipoprotein processing by signal peptidase II in the Gram-positive eubacterium Bacillus subtilis - Signal peptidase II is required for the efficient secretion of alpha-amylase, a non-lipoprotein

Computer-assisted analyses indicate that Bacillus subtilis contains approxi mately 300 genes for exported proteins with an amino-terminal signal peptid e. About 114 of these are lipoproteins, which are retained in the cytoplasm ic membrane. We have investigated the importance of lipoprotein processing by signal peptidase II (SPase II) for cellular homeostasis, using cells lac king SPase II. The results show that lipoprotein processing is important fo r cell viability at low and high temperatures, suggesting that lipoproteins are essential for growth under these conditions. Although certain lipoprot eins are required for the development of genetic competence, sporulation, a nd germination, these developmental processes were not affected in the abse nce of SPase II. Cells lacking SPase II accumulated lipid-modified precurso r and mature-like forms of PrsA, a folding catalyst for secreted proteins. These forms of PrsA seem to have a reduced activity, as the secretion of al pha-amylase was strongly impaired. Unexpectedly, type I signal peptidases, which process secretory preproteins, were not involved in alternative amino -terminal processing of pre-PrsA in the absence of SPase II. In conclusion, processing of Lipoproteins by SPase II in B, subtilis is not strictly requ ired for lipoprotein function, which is surprising as lipoproteins and type II SPases seem to be conserved in all eubacteria.