Department of Biosciences, University of Oslo, Blindernveien 31, 0371, Oslo, Norway.
Max Planck Institute for Developmental Biology, Department 1, 72076, Tübingen, Germany.
Mol Microbiol. 2019 Mar;111(3):844-862. doi: 10.1111/mmi.14195. Epub 2019 Feb 13.
Trimeric autotransporter adhesins (TAAs) are a subset of a larger protein family called the type V secretion systems. They are localized on the cell surface of Gram-negative bacteria, function as mediators of attachment to inorganic surfaces and host cells, and thus include important virulence factors. Yersinia adhesin A (YadA) from Yersinia enterocolitica is a prototypical TAA that is used extensively to study the structure and function of the type Vc secretion system. A solid-state NMR study of the membrane anchor domain of YadA previously revealed a flexible stretch of small residues, termed the ASSA region, that links the membrane anchor to the stalk domain. In this study, we present evidence that single amino acid proline substitutions produce two different conformers of the membrane anchor domain of YadA; one with the N-termini facing the extracellular surface, and a second with the N-termini located in the periplasm. We propose that TAAs adopt a hairpin intermediate during secretion, as has been shown before for other subtypes of the type V secretion system. As the YadA transition state intermediate can be isolated from the outer membrane, future structural studies should be possible to further unravel details of the autotransport process.
三聚体自转运黏附素（TAAs）是一种称为 V 型分泌系统的更大蛋白质家族的一个子集。它们定位于革兰氏阴性细菌的细胞表面，作为与无机表面和宿主细胞附着的介质，因此包括重要的毒力因子。来自肠侵袭性大肠杆菌的耶尔森氏菌黏附素 A（YadA）是一种典型的 TAA，被广泛用于研究 Vc 型分泌系统的结构和功能。以前对 YadA 的膜锚定域的固态 NMR 研究揭示了一个称为 ASSA 区的柔性小残基延伸段，它将膜锚定与柄部连接起来。在这项研究中，我们提供了证据表明，单个氨基酸脯氨酸取代会产生 YadA 膜锚定域的两种不同构象；一种构象的 N 末端朝向细胞外表面，另一种构象的 N 末端位于周质中。我们提出 TAA 在分泌过程中采用发夹中间体，这与其他 V 型分泌系统亚型的情况一致。由于可以从外膜中分离出 YadA 的过渡态中间体，因此未来的结构研究应该有可能进一步揭示自转运过程的细节。
