Institute of Medical Microbiology, University Hospital of Münster, Münster, Germany.
PLoS One. 2012;7(6):e40353. doi: 10.1371/journal.pone.0040353. Epub 2012 Jun 29.
Staphylococcus aureus is a frequent cause of serious and life-threatening infections, such as endocarditis, osteomyelitis, pneumonia, and sepsis. Its adherence to various host structures is crucial for the establishment of diseases. Adherence may be mediated by a variety of adhesins, among them the autolysin/adhesins Atl and Aaa. Aaa is composed of three N-terminal repeated sequences homologous to a lysin motif (LysM) that can confer cell wall attachment and a C-terminally located cysteine, histidine-dependent amidohydrolase/peptidase (CHAP) domain having bacteriolytic activity in many proteins.
METHODOLOGY/PRINCIPAL FINDINGS: Here, we show by surface plasmon resonance that the LysM domain binds to fibrinogen, fibronectin, and vitronectin respresenting a novel adhesive function for this domain. Moreover, we demonstrated that the CHAP domain not only mediates the bacteriolytic activity, but also adherence to fibrinogen, fibronectin, and vitronectin, thus demonstrating for the first time an adhesive function for this domain. Adherence of an S. aureus aaa mutant and the complemented aaa mutant is slightly decreased and increased, respectively, to vitronectin, but not to fibrinogen and fibronectin, which might at least in part result from an increased expression of atl in the aaa mutant. Furthermore, an S. aureus atl mutant that showed enhanced adherence to fibrinogen, fibronectin, and endothelial cells also demonstrated increased aaa expression and production of Aaa. Thus, the redundant functions of Aaa and Atl might at least in part be interchangeable. Lastly, RT-PCR and zymographic analysis revealed that aaa is negatively regulated by the global virulence gene regulators agr and SarA.
CONCLUSIONS/SIGNIFICANCE: We identified novel functions for two widely distributed protein domains, LysM and CHAP, i.e. the adherence to the extracellular matrix proteins fibrinogen, fibronectin, and vitronectin. The adhesive properties of Aaa might promote S. aureus colonization of host extracellular matrix and tissue, suggesting a role for Aaa in the pathogenesis of S. aureus infections.
金黄色葡萄球菌是一种常见的致病菌，可引起严重的、危及生命的感染，如心内膜炎、骨髓炎、肺炎和败血症。其对各种宿主结构的黏附对于疾病的发生至关重要。黏附作用可能由多种黏附素介导，其中包括自溶素/黏附素 Atl 和 Aaa。Aaa 由三个与溶菌酶基序（LysM）同源的 N 端重复序列组成，该基序可赋予细胞壁附着功能，以及 C 端定位的半胱氨酸、组氨酸依赖性氨肽酶/肽酶（CHAP）结构域，该结构域在许多蛋白质中具有溶菌活性。
方法/主要发现：在这里，我们通过表面等离子体共振显示 LysM 结构域结合纤维蛋白原、纤维连接蛋白和 vitronectin，代表该结构域的新的黏附功能。此外，我们证明 CHAP 结构域不仅介导溶菌活性，还介导对纤维蛋白原、纤维连接蛋白和 vitronectin 的黏附作用，从而首次证明该结构域具有黏附作用。金黄色葡萄球菌 aaa 突变体和互补的 aaa 突变体对 vitronectin 的黏附作用略有降低和增加，而对纤维蛋白原和纤维连接蛋白则没有，这至少部分是由于 aaa 突变体中 atl 的表达增加所致。此外，对纤维蛋白原、纤维连接蛋白和内皮细胞的黏附作用增强的金黄色葡萄球菌 atl 突变体也表现出 aaa 表达和 Aaa 产生增加。因此，Aaa 和 Atl 的冗余功能至少在一定程度上是可以互换的。最后，RT-PCR 和酶谱分析显示，agr 和 SarA 等全局毒力基因调节剂对 aaa 进行负调控。
结论/意义：我们鉴定了两个广泛分布的蛋白结构域 LysM 和 CHAP 的新功能，即对细胞外基质蛋白纤维蛋白原、纤维连接蛋白和 vitronectin 的黏附作用。Aaa 的黏附特性可能促进金黄色葡萄球菌对宿主细胞外基质和组织的定植，提示 Aaa 在金黄色葡萄球菌感染的发病机制中起作用。
