Correlation of in situ mechanosensitive responses of the Moraxella catarrhalis adhesin UspA1 with fibronectin and receptor CEACAM1 binding
Correlation of in situ mechanosensitive responses of the Moraxella catarrhalis adhesin UspA1 with fibronectin and receptor CEACAM1 binding
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DOI：
10.1073/pnas.1106341108
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发表时间：
2011-09-13
影响因子：
11.1
通讯作者：
Brady, R. Leo
中科院分区：
文献类型：
--
作者：
Agnew, Christopher;Borodina, Elena;Brady, R. Leo
细菌细胞表面通常有一层由黏附蛋白的多个拷贝组成的装饰层，黏附蛋白的结合相互作用启动定植和感染过程。在这项研究中，我们研究了来自人类中耳感染病原体卡他莫拉菌的UspA1粘附蛋白的物理可变形性。UspA1结合一系列细胞外蛋白，包括纤维连接蛋白和上皮细胞受体癌胚抗原相关细胞粘附分子1 （CEACAM1）。电镜显示，未配位的UspA1在莫拉菌表面密集排列，并从莫拉菌表面延伸约800埃。使用改进的原子力显微镜，我们发现在添加纤维连接蛋白或CEACAM1时，细胞表面的UspA1层的粘附性能和厚度会发生变化。这种原位分析然后与UspA1的分子结构相关联。为了提供UspA1的整体模型，我们确定了两个n端片段的晶体结构，然后将其与ceacam1结合位点的先前结构结合。我们发现UspA1-纤维连接蛋白复合物是在UspA1头部区域和纤维连接蛋白的第13个iii型结构域之间形成的，并且使用x射线散射，该复合物涉及这两个蛋白之间的角关联。结合先前的研究，CEACAM1-UspA1复合物在溶液中明显弯曲，我们将这些对UspA1分离片段的观察与其在细胞表面的原位反应联系起来。因此，这项研究提供了细胞表面蛋白质构象变化的罕见直接演示。
Bacterial cell surfaces are commonly decorated with a layer formed from multiple copies of adhesin proteins whose binding interactions initiate colonization and infection processes. In this study, we investigate the physical deformability of the UspA1 adhesin protein from Moraxella catarrhalis, a causative agent of middle-ear infections in humans. UspA1 binds a range of extracellular proteins including fibronectin, and the epithelial cellular receptor carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1). Electron microscopy indicates that unliganded UspA1 is densely packed at, and extends about 800 angstrom from, the Moraxella surface. Using a modified atomic force microscope, we show that the adhesive properties and thickness of the UspA1 layer at the cell surface varies on addition of either fibronectin or CEACAM1. This in situ analysis is then correlated with the molecular structure of UspA1. To provide an overall model for UspA1, we have determined crystal structures for two N-terminal fragments which are then combined with a previous structure of the CEACAM1-binding site. We show that the UspA1-fibronectin complex is formed between UspA1 head region and the 13th type-III domain of fibronectin and, using X-ray scattering, that the complex involves an angular association between these two proteins. In combination with a previous study, which showed that the CEACAM1-UspA1 complex is distinctively bent in solution, we correlate these observations on isolated fragments of UspA1 with its in situ response on the cell surface. This study therefore provides a rare direct demonstration of protein conformational change at the cell surface.