Van Molle Inge, Moonens Kristof, Buts Lieven, Garcia-Pino Abel, Panjikar Santosh, Wyns Lode, De Greve Henri, Bouckaert Julie
Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, Brussels, Belgium.
Acta Crystallogr D Biol Crystallogr. 2009 May;65(Pt 5):411-20. doi: 10.1107/S0907444909005174. Epub 2009 Apr 18.
Many Gram-negative bacteria use the chaperone-usher pathway to express adhesive surface structures, such as fimbriae, in order to mediate attachment to host cells. Periplasmic chaperones are required to shuttle fimbrial subunits or pilins through the periplasmic space in an assembly-competent form. The chaperones cap the hydrophobic surface of the pilins through a donor-strand complementation mechanism. FaeE is the periplasmic chaperone required for the assembly of the F4 fimbriae of enterotoxigenic Escherichia coli. The FaeE crystal structure shows a dimer formed by interaction between the pilin-binding interfaces of the two monomers. Dimerization and tetramerization have been observed previously in crystal structures of fimbrial chaperones and have been suggested to serve as a self-capping mechanism that protects the pilin-interactive surfaces in solution in the absence of the pilins. However, thermodynamic and biochemical data show that FaeE occurs as a stable monomer in solution. Other lines of evidence indicate that self-capping of the pilin-interactive interfaces is not a mechanism that is conservedly applied by all periplasmic chaperones, but is rather a case-specific solution to cap aggregation-prone surfaces.
许多革兰氏阴性菌利用伴侣-外膜蛋白途径来表达黏附性表面结构，如菌毛，以便介导与宿主细胞的黏附。周质伴侣蛋白需要以具备组装能力的形式将菌毛亚基或菌毛蛋白穿梭运输穿过周质空间。伴侣蛋白通过供体链互补机制覆盖菌毛蛋白的疏水表面。FaeE是产肠毒素大肠杆菌F4菌毛组装所需的周质伴侣蛋白。FaeE晶体结构显示由两个单体的菌毛蛋白结合界面之间相互作用形成的二聚体。先前在菌毛伴侣蛋白的晶体结构中观察到二聚化和四聚化现象，并有人提出这可作为一种自我封闭机制，在没有菌毛蛋白的情况下保护溶液中菌毛蛋白的相互作用表面。然而，热力学和生化数据表明FaeE在溶液中以稳定的单体形式存在。其他证据表明，菌毛蛋白相互作用界面的自我封闭并非所有周质伴侣蛋白都普遍采用的机制，而是针对易聚集表面进行封闭的一种特定情况的解决方案。
