A PhoP/PhoQ-induced lipase (PagL) that catalyzes 3-O-deacylation of lipid a precursors in membranes of Salmonella typhimurium

Pathogenic bacteria modify the structure of the lipid A portion of their li popolysaccharide in response to environmental changes. Some lipid A modific ations are important for virulence and resistance to cationic antimicrobial peptides. The two-component system PhoP/PhoQ plays a central role in regul ating lipid A modification. We now report the discovery of a PhoP/PhoQ-acti vated gene (pagL) in Salmonella typhimurium, encoding a deacylase that remo ves the R-3-hydroxymyristate moiety attached at position 3 of certain lipid A precursors. The deacylase gene (pagL) was identified by assaying for los s of deacylase activity in extracts of 14 random TnphoA::pag insertion muta nts. The pagL gene encodes a protein of 185 amino acid residues unique to S . typhimurium and closely related organisms such as Salmonella typhi. Heter ologous expression of pagL in Escherichia coli on plasmid pWLP21 results in loss of the R-3-hydroxymyristate moiety at position 3 in similar to 90% of the lipid A molecules but does not inhibit cell growth. PagL is synthesize d with a 20-amino acid N-terminal signal peptide and is localized mainly in the outer membrane, as judged by assays of separated S. typhimurium membra nes and by SDS-polyacrylamide gel analysis of membranes from E. coli cells that overexpress PagL. The function of PagL is unknown, given that S. typhi murium mutants lacking pagL display no obvious phenotypes, but PagL might n evertheless play a role in pathogenesis if it serves to modulate the cytoki ne response of an infected animal host.