The uncontrolled formation of amyloid fibers is the hallmark of more than twenty human diseases. In contrast to disease-associated amyloids, which are the products of protein misfolding, E. coli assembles functional amyloid fibers called curli on its surface using an elegant biogenesis machine. Composed of a major subunit, CsgA, and a minor subunit, CsgB, curli play important roles in host cell adhesion, long-term survival and other bacterial community behaviors. Assembly of curli fibers is a template-directed conversion process where membrane-tethered CsgB initiates CsgA polymerization. The CsgA amyloid core is composed of five imperfect repeating units. In a series of in vivo and in vitro experiments, we determined the sequence and structural determinants that guide the initiation and propagation of CsgA polymers. The CsgA N- and C-terminal repeating units govern its polymerization and responsiveness to CsgB. Specifically, conserved glutamine and asparagine residues present in the CsgA N- and C-terminal repeating units are required for CsgB-mediated nucleation and efficient self-assembly.

中文翻译：

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Curli 提供了理解受控淀粉样蛋白传播的模板。

淀粉样蛋白纤维不受控制的形成是二十多种人类疾病的标志。与疾病相关的淀粉样蛋白（蛋白质错误折叠的产物）相反，大肠杆菌使用优雅的生物发生机器在其表面组装称为 curl 的功能性淀粉样蛋白纤维。卷曲由主要亚基 CsgA 和次要亚基 CsgB 组成，在宿主细胞粘附、长期存活和其他细菌群落行为中发挥重要作用。卷曲纤维的组装是一种模板导向的转化过程，其中膜束缚的 CsgB 引发 CsgA 聚合。CsgA 淀粉样蛋白核心由五个不完美的重复单元组成。在一系列体内和体外实验中，我们确定了指导 CsgA 聚合物起始和传播的序列和结构决定因素。CsgA N 端和 C 端重复单元控制其聚合和对 CsgB 的响应。具体而言，CsgB 介导的成核和有效的自组装需要 CsgA N 端和 C 端重复单元中存在的保守谷氨酰胺和天冬酰胺残基。