PMID:24391051

Citation	Xiao, Y and Wall, D' (2014) Genetic redundancy, proximity and functionality of lspA, the target of antibiotic TA, in the Myxococcus xanthus producer strain. J. Bacteriol. '
Abstract	We recently showed that type II signal peptidase (SPaseII) encoded by lspA is the target of an antibiotic called TA (myxovirescin), which is made by Myxococcus xanthus. SPaseII cleaves the signal peptide during bacterial lipoprotein processing. Bacteria typically contain one lspA gene; however, strikingly, the M. xanthus DK1622 genome contains four (lspA1-4). Since two of these genes, lspA3 and lspA4, are located in the giant TA biosynthetic gene cluster, we hypothesized they may play a role in TA resistance. To investigate the function of the four lspA(Mx) genes we conducted sequence comparisons and found that they contained nearly all the conserved residues characteristic of SPaseII family members. Genetic studies found that an Escherichia coli ΔlspA mutation could be complemented by any of the lspA(Mx) genes in an lpp mutant background, but not in an E. coli lpp(+) background. Because Lpp is the most abundant E. coli lipoprotein, these results suggest the M. xanthus proteins do not function as efficiently as the host enzyme. In E. coli, overexpression of the LspA(Mx) proteins each conferred TA and globomycin resistance, although LspA3 conferred the highest degree of resistance. In M. xanthus each lspA(Mx) gene could be deleted and was therefore dispensable for growth. However, lspA3 or lspA4 deletion mutants each exhibited a tan phase variation bias, which likely accounts for their reduced swarming and delayed development phenotypes. In summary, we propose that all four LspA(Mx) proteins function as SPaseIIs, and that LspA3 and LspA4 might also have roles in TA(r) and regulation, respectively.
Links	PubMed Online version:10.1128/JB.01361-13
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