Department of Protein Evolution, Max Planck Institute for Developmental Biology, 72076 Tübingen, Germany.
Proc Natl Acad Sci U S A. 2012 Dec 18;109(51):20907-12. doi: 10.1073/pnas.1211872110. Epub 2012 Dec 3.
Trimeric autotransporter adhesins (TAAs) are modular, highly repetitive surface proteins that mediate adhesion to host cells in a broad range of Gram-negative pathogens. Although their sizes may differ by more than one order of magnitude, they all follow the same basic head-stalk-anchor architecture, where the head mediates adhesion and autoagglutination, the stalk projects the head from the bacterial surface, and the anchor provides the export function and attaches the adhesin to the bacterial outer membrane after export is complete. In complex adhesins, head and stalk domains may alternate several times before the anchor is reached. Despite extensive sequence divergence, the structures of TAA domains are highly constrained, due to the tight interleaving of their constituent polypeptide chains. We have therefore taken a "domain dictionary" approach to characterize representatives for each domain type by X-ray crystallography and use these structures to reconstruct complete TAA fibers. With SadA from Salmonella enterica, EhaG from enteropathogenic Escherichia coli (EHEC), and UpaG from uropathogenic E. coli (UPEC), we present three representative structures of a complex adhesin that occur in a conserved genomic context in Enterobacteria and is essential in the infection process of uropathogenic E. coli. Our work proves the applicability of the dictionary approach to understanding the structure of a class of proteins that are otherwise poorly tractable by high-resolution methods and provides a basis for the rapid and detailed annotation of newly identified TAAs.
三聚体自转运黏附素（TAAs）是一种模块化、高度重复的表面蛋白，能介导多种革兰氏阴性病原体与宿主细胞的黏附。尽管它们的大小可能相差一个数量级以上，但它们都遵循相同的基本头部-茎干-锚定结构，其中头部介导黏附与自身聚集，茎干将头部从细菌表面伸出，锚定提供输出功能，并在输出完成后将黏附素附着到细菌外膜上。在复杂黏附素中，头部和茎干结构可能在到达锚定结构之前交替多次。尽管存在广泛的序列差异，但由于其组成多肽链的紧密交错，TAA 结构域的结构受到高度限制。因此，我们采用“结构域字典”方法，通过 X 射线晶体学对每种结构域类型的代表进行特征描述，并使用这些结构来重建完整的 TAA 纤维。我们展示了三种复杂黏附素的代表结构，它们存在于肠杆菌科中保守的基因组环境中，对于尿路致病性大肠杆菌的感染过程是必不可少的。我们的工作证明了字典方法在理解一类结构蛋白方面的适用性，这些结构蛋白用高分辨率方法很难处理，并为新发现的 TAAs 的快速和详细注释提供了基础。
