Wainwright L A, Kaper J B
Center for Vaccine Development, Department of Medicine, University of Maryland School of Medicine, Baltimore 21201, USA.
Mol Microbiol. 1998 Mar;27(6):1247-60. doi: 10.1046/j.1365-2958.1998.00771.x.
Enteropathogenic Escherichia coli uses a type III secretion apparatus to deliver proteins essential for pathogenesis to the host epithelium. Several proteins have been detected in culture supernatants of the prototype EPEC strain E2348/69 and three of these, EspA, EspB, and EspD, use type III machinery for export. Here, we report the identification and characterization of CesD, a protein required for proper EspB and EspD secretion. CesD shows sequence homology to chaperone proteins from other type III secretion pathways. Based on this, we hypothesize that CesD may function as a secretion chaperone in EPEC. A mutation in cesD abolished EspD secretion into culture supernatants and reduced the amount of secreted EspB, but had little effect on the amount of secreted EspA. The mutant strain was negative for both FAS and Tir phosphorylation, consistent with the previously described roles for EspB and EspD in EPEC pathogenesis. CesD was shown to interact with EspD but not EspB or EspA. CesD was detected in the bacterial cytosol, and, surprisingly, a substantial amount of the protein was also found to be associated with the inner membrane. Thus, although CesD has some attributes that are similar to other type III secretion chaperones, its membrane localization separates it from previously described members of this family.
肠致病性大肠杆菌利用III型分泌装置将致病所需的蛋白质递送至宿主上皮细胞。在原型肠致病性大肠杆菌菌株E2348/69的培养上清液中已检测到几种蛋白质，其中三种，即EspA、EspB和EspD，利用III型机制进行分泌。在此，我们报告了CesD的鉴定和特性，CesD是EspB和EspD正常分泌所必需的一种蛋白质。CesD与其他III型分泌途径的伴侣蛋白具有序列同源性。基于此，我们推测CesD可能在肠致病性大肠杆菌中作为一种分泌伴侣发挥作用。cesD中的一个突变消除了EspD分泌到培养上清液中的能力，并减少了分泌的EspB的量，但对分泌的EspA的量影响很小。该突变菌株在FAS和Tir磷酸化方面均为阴性，这与之前描述的EspB和EspD在肠致病性大肠杆菌发病机制中的作用一致。已证明CesD与EspD相互作用，但不与EspB或EspA相互作用。在细菌胞质溶胶中检测到了CesD，令人惊讶的是，还发现大量该蛋白质与内膜相关。因此，尽管CesD具有一些与其他III型分泌伴侣相似的特性，但其膜定位使其与该家族先前描述的成员有所不同。
