Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Laboratory of Intracellular Parasites, NIAID, National Institutes of Health Rocky Mountain Laboratories, Hamilton, Montana, USA.
Infect Immun. 2014 Jul;82(7):2935-48. doi: 10.1128/IAI.00102-14. Epub 2014 Apr 28.
The Francisella FTT0831c/FTL_0325 gene encodes amino acid motifs to suggest it is a lipoprotein and that it may interact with the bacterial cell wall as a member of the OmpA-like protein family. Previous studies have suggested that FTT0831c is surface exposed and required for virulence of Francisella tularensis by subverting the host innate immune response (M. Mahawar et al., J. Biol. Chem. 287:25216-25229, 2012). We also found that FTT0831c is required for murine pathogenesis and intramacrophage growth of Schu S4, but we propose a different model to account for the proinflammatory nature of the resultant mutants. First, inactivation of FTL_0325 from live vaccine strain (LVS) or FTT0831c from Schu S4 resulted in temperature-dependent defects in cell viability and morphology. Loss of FTT0831c was also associated with an unusual defect in lipopolysaccharide O-antigen synthesis, but loss of FTL_0325 was not. Full restoration of these properties was observed in complemented strains expressing FTT0831c in trans, but not in strains lacking the OmpA motif, suggesting that cell wall contact is required. Finally, growth of the LVS FTL_0325 mutant in Mueller-Hinton broth at 37°C resulted in the appearance of membrane blebs at the poles and midpoint, prior to the formation of enlarged round cells that showed evidence of compromised cellular membranes. Taken together, these data are more consistent with the known structural role of OmpA-like proteins in linking the OM to the cell wall and, as such, maintenance of structural integrity preventing altered surface exposure or release of Toll-like receptor 2 agonists during rapid growth of Francisella in vitro and in vivo.
弗朗西斯氏菌 FTT0831c/FTL_0325 基因编码的氨基酸模体表明它是一种脂蛋白，可能作为 OmpA 样蛋白家族的一员与细菌细胞壁相互作用。先前的研究表明，FTT0831c 是表面暴露的，并且通过颠覆宿主先天免疫反应，对土拉弗朗西斯菌的毒力是必需的（M. Mahawar 等人，J. Biol. Chem. 287:25216-25229, 2012）。我们还发现 FTT0831c 是鼠致病和 Schu S4 内巨噬细胞生长所必需的，但我们提出了一个不同的模型来解释由此产生的突变体的促炎性质。首先，活疫苗株（LVS）中 FTL_0325 的失活或 Schu S4 中 FTT0831c 的失活导致细胞活力和形态的温度依赖性缺陷。FTT0831c 的缺失也与脂多糖 O-抗原合成的异常缺陷有关，但 FTL_0325 的缺失没有。在互补菌株中表达 FTT0831c 可完全恢复这些特性，但在缺乏 OmpA 模体的菌株中则不能，这表明需要与细胞壁接触。最后，在 37°C 的 Mueller-Hinton 肉汤中生长的 LVS FTL_0325 突变株导致在形成大的圆形细胞之前，在极点和中点出现膜泡，这些细胞显示出细胞膜受损的证据。综上所述，这些数据更符合 OmpA 样蛋白在连接 OM 与细胞壁方面的已知结构作用，因此，在弗朗西斯菌在体外和体内快速生长过程中，维持结构完整性可以防止表面暴露的改变或 Toll 样受体 2 激动剂的释放。
