Gilbert Harry J
Institute for Cell and Molecular Biosciences, Newcastle University, The Medical School, Framlington Place, Newcastle upon Tyne NE2 4HH, UK.
Mol Microbiol. 2007 Mar;63(6):1568-76. doi: 10.1111/j.1365-2958.2007.05640.x.
The assembly of proteins that display complementary activities into supramolecular intra- and extracellular complexes is central to cellular function. One such nanomachine of considerable biological and industrial significance is the plant cell wall degrading apparatus of anaerobic bacteria termed the cellulosome. The Clostridium thermocellum cellulosome assembles through the interaction of a type I dockerin module in the catalytic entities with one of several type I cohesin modules in the non-catalytic scaffolding protein. Recent structural studies have provided the molecular details of how dockerin-cohesin interactions mediate both cellulosome assembly and the retention of the protein complex on the bacterial cell surface. The type I dockerin, which displays near-perfect sequence and structural symmetry, interacts with its cohesin partner through a dual binding mode in which either the N- or C-terminal helix dominate heterodimer formation. The biological significance of this dual binding mode is discussed with respect to the plasticity of the orientation of the catalytic subunits within this supramolecular assembly. The flexibility in the quaternary structure of the cellulosome may reflect the challenges presented by the degradation of a heterogenous recalcitrant insoluble substrate by an intricate macromolecular complex, in which the essential synergy between the catalytic subunits is a key feature of cellulosome function.
将具有互补活性的蛋白质组装成超分子细胞内和细胞外复合物是细胞功能的核心。一种具有重要生物学和工业意义的纳米机器是厌氧细菌的植物细胞壁降解装置，称为纤维小体。嗜热栖热放线菌纤维小体通过催化实体中的I型锚定蛋白模块与非催化支架蛋白中的几种I型粘着蛋白模块之一相互作用而组装。最近的结构研究提供了分子细节，说明锚定蛋白-粘着蛋白相互作用如何介导纤维小体组装以及蛋白质复合物在细菌细胞表面的保留。I型锚定蛋白具有近乎完美的序列和结构对称性，通过双重结合模式与其粘着蛋白伴侣相互作用，其中N端或C端螺旋主导异二聚体形成。关于该超分子组装中催化亚基取向的可塑性，讨论了这种双重结合模式的生物学意义。纤维小体四级结构的灵活性可能反映了由复杂的大分子复合物降解异质难溶性底物所带来的挑战，其中催化亚基之间的基本协同作用是纤维小体功能的关键特征。
