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Cryo-EM structure of the CFA/I pilus rod

机译：CFA / I毛发棒的Cryo-EM结构

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Enterotoxigenic Escherichia coli (ETEC) are common agents of diarrhea for travelers and a major cause of mortality in children in developing countries. To attach to intestinal cells ETEC express colonization factors, among them CFA/I, which are the most prevalent factors and are the archetypical representative of class 5 pili. The helical quaternary structure of CFA/I can be unwound under tensile force and it has been shown that this mechanical property helps bacteria to withstand shear forces from fluid motion. We report in this work the CFA/I pilus structure at 4.3 Å resolution from electron cryomicroscopy (cryo-EM) data, and report details of the donor strand complementation. The CfaB pilins modeled into the cryo-EM map allow us to identify the buried surface area between subunits, and these regions are correlated to quaternary structural stability in class 5 and chaperone–usher pili. In addition, from the model built using the EM structure we also predicted that residue 13 (proline) of the N-terminal β-strand could have a major impact on the filament's structural stability. Therefore, we used optical tweezers to measure and compare the stability of the quaternary structure of wild type CFA/I and a point-mutated CFA/I with a propensity for unwinding. We found that pili with this mutated CFA/I require a lower force to unwind, supporting our hypothesis that Pro13 is important for structural stability. The high-resolution CFA/I pilus structure presented in this work and the analysis of structural stability will be useful for the development of novel antimicrobial drugs that target adhesion pili needed for initial attachment and sustained adhesion of ETEC.
机译：肠毒素大肠杆菌（ETEC）是旅行者腹泻的常见病原，也是发展中国家儿童死亡的主要原因。为了附着在肠细胞上，ETEC表达定植因子，其中CFA / I是最普遍的因子，是5类菌毛的典型代表。 CFA / I的螺旋四元结构可以在拉力作用下解开，并且已经证明该机械性能有助于细菌抵抗流体运动产生的剪切力。我们在这项工作中报告从电子冷冻显微镜（cryo-EM）数据以4.3Å分辨率解析出CFA / I菌毛结构，并报告了供体链互补的细节。建模到cryo-EM图中的CfaB菌毛素使我们能够识别亚基之间的掩埋表面积，并且这些区域与5类和伴侣-菌落菌毛的四级结构稳定性相关。此外，从使用EM结构建立的模型中，我们还预测N末端β链的13位残基（脯氨酸）可能对灯丝的结构稳定性产生重大影响。因此，我们使用光镊来测量和比较野生型CFA / I和具有突变倾向的点突变CFA / I的四级结构的稳定性。我们发现具有这种突变的CFA / I的菌毛需要较小的力才能解开，这支持了我们的假设，即Pro13对结构稳定性很重要。这项工作中提出的高分辨率CFA / I菌毛结构和结构稳定性分析将有助于开发靶向ETEC初始附着和持续粘附所需的粘附菌毛的新型抗菌药物。

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