Research for outer membrane remodeling in Salmonella enterica

肠炎沙门氏菌血清型鼠伤寒沙门氏菌改变其脂多糖（LPS），包括脂质A部分，以响应其环境的变化，包括宿主组织。脂质A 3- o -去乙酰化酶PagL在模拟宿主环境下促进表达，在肠球菌中表现出潜伏期；尽管外膜蛋白PagL表达，但在体内通常不观察到脂质A的去酰化。相比之下，PagL在肠链球菌pmrA和pmrE突变体中不表现出潜伏期，这两种突变体都缺乏基于阿拉伯糖氨基修饰的脂质A，这表明阿拉伯糖氨基修饰的LPS物种参与了潜伏期。为了分析PagL的抑制机制，我们产生了位于四个细胞外环的氨基酸残基被丙氨酸取代的PagL突变体。在表达几种PagL突变体的肠链球菌中观察到明显的脂质A 3- o -去酰化，但在表达野生型PagL的肠链球菌中没有观察到，这表明点突变使PagL从潜伏期中释放出来。此外，突变不影响肠链球菌pmrA突变体或大肠杆菌BL21（DE3）中PagL的脂质A 3- o -去乙酰化酶活性。综上所述，这些结果表明，位于PagL细胞外环的特定氨基酸残基参与了对氨基阿拉伯糖修饰的LPS的识别。此外，与表达野生型PagL的肠链球菌相比，表达PagL突变体的肠链球菌在43℃时表现出明显的生长停滞，这表明PagL的潜伏期对细菌生长很重要。

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.