An internal thioester in a pathogen surface protein mediates covalent host binding.
An internal thioester in a pathogen surface protein mediates covalent host binding.
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DOI：
10.7554/elife.06638
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发表时间：
2015-06-02
期刊：
影响因子：
7.7
通讯作者：
Schwarz-Linek U
中科院分区：
文献类型：
--
作者：
Walden M;Edwards JM;Dziewulska AM;Bergmann R;Saalbach G;Kan SY;Miller OK;Weckener M;Jackson RJ;Shirran SL;Botting CH;Florence GJ;Rohde M;Banfield MJ;Schwarz-Linek U
致病微生物和寄生微生物必须附着在组织上才能引起疾病并在宿主中持续存在。定植和感染依赖于宿主-微生物界面上的特定分子相互作用，这些分子相互作用涉及微生物表面蛋白或粘附素。迄今为止，仅已知粘附素与宿主受体非共价结合。在这里，我们表明，链球菌表面蛋白SfbI介导的共价相互作用与宿主蛋白质纤维蛋白原使用不寻常的内部硫酯键作为“化学鱼叉”。在炎症模型中，这种交联反应允许细菌附着于纤维蛋白，SfbI结合于人类细胞。含硫酯结构域出乎意料地普遍存在于革兰氏阳性细菌中，包括许多临床相关的病原体。我们的研究结果支持细菌编码的共价结合作为宿主与微生物相互作用的新分子原理。这代表了一个尚未开发的治疗细菌感染的目标，也可能为工程有益的相互作用提供新的机会。http://dx.doi.org/10.7554/eLife.06638.001人体是数万亿微生物的家园;大多数是无害的，但有些可能导致疾病。为了在宿主体内生存，微生物必须首先附着在宿主组织上。这个过程涉及到每个微生物表面的多种蛋白质，称为粘附素，它们与组成这些组织的分子相互作用。像所有蛋白质一样，粘附素是由称为氨基酸的简单构建单元组成的长链，每个氨基酸通过强“共价”键连接到下一个氨基酸。然而，粘附素通常通过许多弱的“非共价”相互作用的组合强度将细菌附着到宿主分子。最近发现，一种来自化脓性链球菌的细菌的粘附素在其两个氨基酸之间的一个不寻常的位置上含有一种罕见的额外共价键，称为硫酯。S.化脓性链球菌是人类咽喉感染的常见原因，也可能导致危及生命的“食肉病”。瓦尔登，爱德华兹等人现在已经使用了一系列的计算，生物化学，结构生物学和基于细胞的技术，以研究其他具有硫酯键的粘附素更详细。计算搜索发现了数百种含有类似键的细菌蛋白质。其中包括许多来自感染人类的细菌：如肺炎链球菌，这是成人肺炎最常见的原因;和艰难梭菌，这是臭名昭著的导致严重的肠道感染的医院病人。对其中三种蛋白质的三维结构进行了更深入的研究，其中包括一种来自S。化脓性链球菌-揭示了每一种都具有明显的硫酯键。对另外九种已鉴定蛋白质的生化测试强烈表明它们也含有硫酯键。瓦尔登，爱德华兹等人随后表明，SfbI不仅能够像传统的粘附素一样附着在组织上，而且还能够与纤维蛋白原发生化学反应：纤维蛋白原是一种对血液凝固至关重要的人类蛋白质，通常在发炎组织和愈合伤口中发现。这种化学反应导致SfbI和纤维蛋白原之间形成共价键，其与连接蛋白质链中氨基酸的键一样稳定。进一步的实验表明，SfbI在模拟组织炎症的条件下与实验室中生长的人类细胞强烈结合。最后，瓦尔登、爱德华兹等人制造了一种不含硫酯的SfbI突变体，发现它不能与纤维蛋白原相互作用，也不能与人类细胞结合。总之，这些发现表明，细菌粘附素中的硫酯就像“化学鱼叉”，微生物可以利用它将自己不可逆地附着在宿主组织内的分子上。这种附着机制以前在宿主-微生物相互作用中从未见过，现在需要进一步的研究来探索干扰这一过程是否可以代表一种治疗细菌感染的新方法。DOI：http://dx.doi.org/10.7554/eLife.06638.002网站
To cause disease and persist in a host, pathogenic and commensal microbes must adhere to tissues. Colonization and infection depend on specific molecular interactions at the host-microbe interface that involve microbial surface proteins, or adhesins. To date, adhesins are only known to bind to host receptors non-covalently. Here we show that the streptococcal surface protein SfbI mediates covalent interaction with the host protein fibrinogen using an unusual internal thioester bond as a ‘chemical harpoon’. This cross-linking reaction allows bacterial attachment to fibrin and SfbI binding to human cells in a model of inflammation. Thioester-containing domains are unexpectedly prevalent in Gram-positive bacteria, including many clinically relevant pathogens. Our findings support bacterial-encoded covalent binding as a new molecular principle in host-microbe interactions. This represents an as yet unexploited target to treat bacterial infection and may also offer novel opportunities for engineering beneficial interactions. DOI: http://dx.doi.org/10.7554/eLife.06638.001 The human body is home to many trillions of microbes; most are harmless, but some may cause disease. To live inside a host, microbes must first attach to host tissues. This process involves multiple proteins on each microbe's surface, called adhesins, which interact with the molecules that make up these tissues. Like all proteins, adhesins are long chains of simpler building blocks called amino acids, and each amino acid is connected to the next via a strong ‘covalent’ bond. Adhesins, however, typically attach bacteria to host molecules through the combined strength of many weak ‘non-covalent’ interactions. It was recently discovered that one adhesin from a bacterium called Streptococcus pyogenes contains a rare, extra covalent bond—called a thioester—in an unusual location between two of its amino acids. S. pyogenes is a common cause of throat infections in humans, and can also cause the life-threatening ‘flesh-eating disease’. Walden, Edwards et al. have now used a range of computational, biochemical, structural biology and cell-based techniques to study other adhesins that have thioester bonds in more detail. Computational searches identified hundreds of bacterial proteins containing similar bonds. These included many from bacteria that infect humans: such as Streptococcus pneumoniae, which is the most common cause of pneumonia in adults; and Clostridium difficile, which is notorious for causing severe gut infections in hospital patients. Closer examination of the three-dimensional structures of three of these proteins—including one called SfbI from S. pyogenes—revealed that each had a clear thioester bond. Biochemical tests of an additional nine of the identified proteins strongly suggested they too contained thioester bonds. Walden, Edwards et al. then showed that SfbI was able to not only attach to tissues like conventional adhesins, but also chemically react with fibrinogen: a human protein that is essential for blood clotting and commonly found in inflamed tissues and healing wounds. This chemical reaction results in the formation of a covalent bond between SfbI and fibrinogen, which is as stable as the bonds that link the amino acids in a protein chain. Further experiments revealed that SfbI strongly binds to human cells grown in the lab under conditions that mimic tissue inflammation. Finally, Walden, Edwards et al. made a mutant version of SfbI that did not contain a thioester, and found that it could not interact with fibrinogen nor bind to human cells. Together, these findings suggest that thioesters in bacterial adhesins act like ‘chemical harpoons’, which microbes can use to irreversibly attach themselves to molecules within their host's tissues. This attachment mechanism has not been seen before in host-microbe interactions, and further research is now needed to explore whether interfering with this process could represent a new way to treat bacterial infections. DOI: http://dx.doi.org/10.7554/eLife.06638.002