美国哥伦比亚大学Alvaro Alonso-Caballero研究小组发现，革兰氏阳性菌可以通过蛋白质折叠调控粘附素与生物表面的结合能力。 这一研究成果于2020年11月30日发表在《自然—化学》上。

在该研究中，课题组通过磁镊力谱技术研究了一种叫Cpa的粘附素的硫酯键在力的作用下的动态变化。当Cpa在小于6 pN的环境中折叠时，其硫酯键可与炎症环境中常见的胺类配体发生可逆反应；反之，机械去折叠化以及暴露在大于6 pN的力中则会阻碍硫酯键重新形成。研究人员认为，这种与蛋白折叠偶合的化学反应开关（即“智能共价键”）可使粘附素在低作用力中与细胞表面的配体可逆结合，而在机械力存在时以共价键形式牢牢锁在细胞表面。

据了解，革兰氏阳性细菌定居在粘膜组织上，并能经受诸如咳嗽带来的机械力扰动，这样的剪切力已经超出了非共价键可以承受的范围。为了克服这些挑战，化脓性链球菌进化出一种叫Cpa的蛋白质，该蛋白是一种具有半胱氨酸-谷氨酰胺硫酯键的纤毛末端粘附素。该硫酯键与宿主细胞表面受体之间的反应使之能够以共价键的方式锚定在细胞表面；另一方面，病原体繁殖又需要不停地在细胞表面迁移和扩散。在此之前，细菌是怎样在分子机理上调和这两个看似矛盾的需求是未知的。

附：英文原文

Title: Protein folding modulates the chemical reactivity of a Gram-positive adhesin

Author: Alvaro Alonso-Caballero, Daniel J. Echelman, Rafael Tapia-Rojo, Shubhasis Haldar, Edward C. Eckels, Julio M. Fernandez

Issue&Volume: 2020-11-30

Abstract: Gram-positive bacteria colonize mucosal tissues, withstanding large mechanical perturbations such as coughing, which generate shear forces that exceed the ability of non-covalent bonds to remain attached. To overcome these challenges, the pathogen Streptococcus pyogenes utilizes the protein Cpa, a pilus tip-end adhesin equipped with a Cys–Gln thioester bond. The reactivity of this bond towards host surface ligands enables covalent anchoring; however, colonization also requires cell migration and spreading over surfaces. The molecular mechanisms underlying these seemingly incompatible requirements remain unknown. Here we demonstrate a magnetic tweezers force spectroscopy assay that resolves the dynamics of the Cpa thioester bond under force. When folded at forces <6pN, the Cpa thioester bond reacts reversibly with amine ligands, which are common in inflammation sites; however, mechanical unfolding and exposure to forces >6pN block thioester reformation. We hypothesize that this folding-coupled reactivity switch (termed a smart covalent bond) could allow the adhesin to undergo binding and unbinding to surface ligands under low force and remain covalently attached under mechanical stress.

DOI: 10.1038/s41557-020-00586-x

Source: https://www.nature.com/articles/s41557-020-00586-x