沙门氏菌在感染过程中调节膜脂,但是在菌血症期间促进其存活的确切蛋白质和机制仍然未知。编码保守的肠道沙门氏菌血清变型鼠伤寒沙门氏菌(STyphimurium)Tol-Paler装置的基因突变引起了外膜(OM)传感器脂蛋白,RcsF,被激活。突变体的胶囊激活表型表明Tol-Pal可能影响包膜脂质稳态。该机制涉及降低OM甘油磷脂(GPL)水平,因为与野生型相比,突变型沙门氏菌在OM内类似地积累磷脂酰甘油(PGl)和磷脂酰乙醇胺(PE)。数据支持大肠杆菌模型,由此Tol-del指导逆行GPL易位穿过周质。鼠伤寒沙门氏菌机制涉及YbgC的贡献,细胞质酰基辅酶A(酰基辅酶A)硫酯酶,还有Cpob,周质TolA结合蛋白。Tol-Pal与YbgC和CpoB之间的功能关系以前尚未解决。鼠伤寒STol-帕尔蛋白类似地促进OM-GPL稳态和Rcs信号不活动,但不同地促进细菌形态,利福平抗性,在巨噬细胞中存活,和小鼠的生存。例如,tolQ,tolR,tola,和cpoB突变体比ybgC明显更减毒,tolB,和pal突变体在疾病的系统小鼠模型中。因此,TolQ存在关键角色,TolR,托拉,和CpoB在小鼠菌血症期间,它们独立于维持GPL稳态。TolQR通道质子穿过内膜(IM)的能力是TolQRA功能所必需的,由于突变保守的面向通道的残基使TolQ在挽救缺失突变表型方面无效。因此,Tol-PAGE促进菌血症期间的鼠伤寒沙门氏菌存活,在某种程度上,通过降低OMGPL浓度,而TolQRA和CpoB通过其他机制增强全身毒力。
Salmonellae regulate membrane lipids during infection, but the exact proteins and mechanisms that promote their survival during bacteremia remain largely unknown. Mutations in genes encoding the conserved Salmonella enterica serovar Typhimurium (S Typhimurium) Tol-Pal apparatus caused the outer membrane (OM) sensor lipoprotein, RcsF, to become activated. The capsule activation phenotype for the mutants suggested that Tol-Pal might influence envelope lipid homeostasis. The mechanism involves reducing OM glycerophospholipid (GPL) levels, since the mutant salmonellae similarly accumulated phosphatidylglycerols (PGl) and phosphatidylethanolamines (PE) within the OM in comparison to the wild type. The data support the Escherichia coli model, whereby Tol-Pal directs retrograde GPL translocation across the periplasm. The S Typhimurium mechanism involves contributions from YbgC, a cytoplasmic acyl coenzyme A (acyl-CoA) thioesterase, and CpoB, a periplasmic TolA-binding protein. The functional relationship between Tol-Pal and YbgC and CpoB was previously unresolved. The S Typhimurium Tol-Pal proteins contribute similarly toward promoting OM-GPL homeostasis and Rcs signaling inactivity but differently toward promoting bacterial morphology, rifampin resistance, survival in macrophages, and survival in mice. For example,
tolQ, tolR, tolA, and cpoB mutants were significantly more attenuated than ybgC, tolB, and pal mutants in a systemic mouse model of disease. Therefore, key roles exist for
TolQ, TolR, TolA, and CpoB during murine bacteremia, which are independent of maintaining GPL homeostasis. The ability of TolQR to channel protons across the inner membrane (IM) is necessary for S Typhimurium TolQRA function, since mutating conserved channel-facing residues rendered
TolQ ineffective at rescuing deletion mutant phenotypes. Therefore, Tol-Pal promotes S Typhimurium survival during bacteremia, in part, by reducing OM GPL concentrations, while TolQRA and CpoB enhance systemic virulence by additional mechanisms.