Research for outer membrane remodeling in Salmonella enterica

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Salmonella enterica serovar Typhimurium modifies its lipopolysaccharide (LPS), including the lipid A portion, in response to changes in its environment including host tissues. The lipid A 3-O-deacylase PagL, the expression of which is promoted under the host-mimetic environment, exhibits latency in S. enterica ; deacylation of lipid A is not usually observed in vivo despite the expression of the outer membrane protein PagL. In contrast, PagL does not exhibit latency in S. enterica pmrA and pmrE mutants, both of which are deficient in the aminoarabinose-based modification of lipid A, indicating that aminoarabinose-modified LPS species were involved in the latency. In order to analyze the machinery for PagL's repression, we generated PagL mutants in which an amino acid residue located at four extracellular loops was replaced with alanine. Apparent lipid A 3-O-deacylation was observed in S. enterica expressing the several PagL mutants, but not in S. enterica expressing wild-type PagL, suggesting that the point mutations released PagL from the latency. In addition, the mutations did not affect lipid A 3-O-deacylase activity of PagL in a S. enterica pmrA mutant or in E. coli BL21(DE3). These results, taken together, indicate that specific amino acid residues located at extracellular loops of PagL are involved in the recognition of aminoarabinose-modified LPS. Furthermore, S enterica expressing the PagL mutants showed apparent growth arrest at 43℃ compared with S. enterica expressing wild-type PagL, indicating that the latency of PagL is important for bacterial growth.