Maturation and processing of SpaI, the lipoprotein involved in subtilin immunity in Bacillus subtilis ATCC 6633

SummarySpaI is a small lipoprotein that provides Bacillus subtilis with autoimmunity against the lantibiotic subtilin. We have investigated the maturation of SpaI through the lipoprotein biosynthesis pathway, and analyzed the consequences of maturations in the acylation of the target lipobox in subtilin immunity. Further specificity of lipid acylation of the cysteine within the conserved sequence of the candidate lipobox (LSAC) was studied by site-directed mutagenesis. The mutants LSAA and LSCA blocked lipid attachment to the SpaI protein. Cell-wall stress-sensing B. subtilis BSF 2470 was exploited to study the function of each mutant upon heterologous expression. This system allowed the monitoring of β-galactosidase activity to the added subtilin at a sublethal dose. Mutants exhibited 2-fold reduction in β-Gal activity, suggesting their contribution in subtilin autoimmunity.