Receptor-binding site as revealed by the crystal structure of CfaE, the colonization factor antigen I fimbrial adhesin of enterotoxigenic Escherichia coli
Receptor-binding site as revealed by the crystal structure of CfaE, the colonization factor antigen I fimbrial adhesin of enterotoxigenic Escherichia coli
复制标题
DOI：
10.1074/jbc.m700921200
复制
发表时间：
2007-08-17
影响因子：
4.8
通讯作者：
Xia, Di
中科院分区：
文献类型：
--
作者：
Li, Yong-Fu;Poole, Steven;Xia, Di
CfaE是产肠毒素大肠杆菌的定植因子抗原I菌毛（CFA/I）的微小的、末端定位的粘附亚基，被认为是在腹泻发病早期产肠毒素大肠杆菌附着在人小肠上所必需的。确定了与CfaE互补的顺式供体链的晶体结构，提供了由替代伴侣途径组装的毛状亚基的第一个原子视图。CfaE结构的顺式供体链互补变体由大小相似的n端粘连蛋白结构域和c端pilin结构域组成，每个结构域都具有可变的免疫球蛋白样褶皱。这两个结构域之间存在广泛的相互作用，似乎使分子变得坚硬。粘附素结构域远端的上表面显示由包括Arg（181）在内的保守残基组成的抑制，这些残基先前被证明是红细胞粘附所必需的。突变分析揭示了一组保守的带正电的残基，这是CFA/ i介导的血凝所必需的，这意味着它是受体结合口袋。簇周围的一些亚类特异性残基的突变对两种用于血凝的红细胞有不同的影响，这表明这些残基在宿主或细胞特异性中起作用。来自主要亚基CfaB的c端供体链折叠为β链，并适合于pilin结构域的疏水沟槽，以完成免疫球蛋白折叠。这条有序的供体链的位置表明了在CFA/I菌毛的原生组装中，下主要菌毛亚基CfaB的位置和方向。
CfaE is the minor, tip-localized adhesive subunit of colonization factor antigen I fimbriae (CFA/I) of enterotoxigenic Escherichia coli and is thought to be essential for the attachment of enterotoxigenic E. coli to the human small intestine early in diarrhea pathogenesis. The crystal structure of an in cis donor strand complemented CfaE was determined, providing the first atomic view of a fimbrial subunit assembled by the alternate chaperone pathway. The in cis donor strand complemented variant of CfaE structure consists of an N-terminal adhesin domain and a C-terminal pilin domain of similar size, each featuring a variable immunoglobulin-like fold. Extensive interactions exist between the two domains and appear to rigidify the molecule. The upper surface of the adhesin domain distal to the pilin domain reveals a depression consisting of conserved residues including Arg(181), previously shown to be necessary for erythrocyte adhesion. Mutational analysis revealed a cluster of conserved, positively charged residues that are required for CFA/I-mediated hemagglutination, implicating this as the receptor-binding pocket. Mutations in a few subclass-specific residues that surround the cluster displayed differential effects on the two red cell species used in hemagglutination, suggesting that these residues play a role in host or cell specificity. The C-terminal donor strand derived from the major subunit CfaB is folded as a beta-strand and fits into a hydrophobic groove in the pilin domain to complete the immunoglobulin fold. The location of this well ordered donor strand suggests the positioning and orientation of the subjacent major fimbrial subunit CfaB in the native assembly of CFA/I fimbriae.