Bhoite Sujeet, van Gerven Nani, Chapman Matthew R, Remaut Han
Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109.
Structural Biology Brussels, Vrije Universiteit Brussel, 1050 Brussels, Belgium.
EcoSal Plus. 2019 Mar;8(2). doi: 10.1128/ecosalplus.ESP-0037-2018.
In 1989, Normark and coworkers reported on fibrous surface structures called curli on strains of that were suspected of causing bovine mastitis. Subsequent work by many groups has revealed an elegant and highly regulated curli biogenesis pathway also referred to as the type VIII secretion system. Curli biogenesis is governed by two divergently transcribed operons, and . The operon encodes the structural subunits of curli, CsgA and CsgB, along with a chaperone-like protein, CsgC. The operon encodes the accessory proteins required for efficient transcription, secretion, and assembly of the curli fiber. CsgA and CsgB are secreted as largely unstructured proteins and transition to β-rich structures that aggregate into regular fibers at the cell surface. Since both of these proteins have been shown to be amyloidogenic in nature, the correct spatiotemporal synthesis of the curli fiber is of paramount importance for proper functioning and viability. Gram-negative bacteria have evolved an elegant machinery for the safe handling, secretion, and extracellular assembly of these amyloidogenic proteins.
1989年，诺马克及其同事报道了一种名为卷曲菌毛的纤维状表面结构，存在于疑似导致牛乳腺炎的菌株中。随后许多研究小组的工作揭示了一种精巧且高度调控的卷曲菌毛生物合成途径，也被称为VIII型分泌系统。卷曲菌毛的生物合成由两个反向转录的操纵子，即csgBAC和csgDEFG控制。csgBAC操纵子编码卷曲菌毛的结构亚基CsgA和CsgB，以及一种类似伴侣蛋白的CsgC。csgDEFG操纵子编码卷曲菌毛纤维高效转录、分泌和组装所需的辅助蛋白。CsgA和CsgB以基本上无结构的蛋白质形式分泌，并转变为富含β折叠的结构，在细胞表面聚集成规则的纤维。由于这两种蛋白质在本质上都已被证明具有淀粉样变性，卷曲菌毛纤维正确的时空合成对于其正常功能和生存能力至关重要。革兰氏阴性菌已经进化出一种精巧的机制，用于安全处理、分泌和在细胞外组装这些淀粉样变性蛋白质。
