Sakellaris H, Balding D P, Scott J R
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Mol Microbiol. 1996 Aug;21(3):529-41. doi: 10.1111/j.1365-2958.1996.tb02562.x.
Some strains of enterotoxigenic Escherichia coli associated with human diarrhoeal disease produce a class of pili represented by those called CS1. For the assembly of the major-pilin subunit, CooA, into pili, each of four linked genes, cooB, A, C, and D, is required. In this study, we have determined the subcellular localization of CooB, C and D, and investigated the molecular interactions of these proteins using specific antisera. CooD appears to be an integral pilus protein because it co-purifies with, and is strongly associated with, CS1 pili. In keeping with its role as an assembly protein, the CooD minor pilin (when overexpressed in CS1-piliated strains) was detected in periplasmic intermolecular complexes with the major-pilin subunit CooA. CooB is an assembly protein found exclusively in the periplasm of CS1-piliated strains. CooB also forms periplasmic intermolecular complexes with CooA, but does not constitute part of the final pilus structure. Immunoblot analysis of cell fractions showed that CooC is an outer membrane protein of CS1-piliated E. coli. Based on this information, we have proposed a model for CS1-pilus assembly which is very similar to the model for polymerization of the PapA pilin of uropathogenic E. coli. As the assembly proteins of Pap and CS1 pili are structurally unrelated, this may represent a case of convergent evolution.
一些与人类腹泻病相关的产肠毒素大肠杆菌菌株会产生一类以CS1菌毛为代表的菌毛。为了将主要菌毛蛋白亚基CooA组装到菌毛中，四个连锁基因cooB、A、C和D中的每一个都是必需的。在本研究中，我们确定了CooB、C和D的亚细胞定位，并使用特异性抗血清研究了这些蛋白质的分子相互作用。CooD似乎是一种完整的菌毛蛋白，因为它与CS1菌毛共纯化并紧密相关。与其作为组装蛋白的作用一致，CooD次要菌毛蛋白（当在产CS1菌毛的菌株中过表达时）在周质分子间复合物中与主要菌毛蛋白亚基CooA一起被检测到。CooB是一种仅在产CS1菌毛菌株的周质中发现的组装蛋白。CooB也与CooA形成周质分子间复合物，但不构成最终菌毛结构的一部分。细胞组分的免疫印迹分析表明，CooC是产CS1菌毛的大肠杆菌的外膜蛋白。基于这些信息，我们提出了一个CS1菌毛组装模型，该模型与致病性大肠杆菌的PapA菌毛聚合模型非常相似。由于Pap菌毛和CS1菌毛的组装蛋白在结构上不相关，这可能代表了趋同进化的一个例子。
