Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22903, USA.
Institut Pasteur, Université Paris Cité, CNRS UMR 6047, Archaeal Virology Unit, 75015 Paris, France.
Cell. 2022 Sep 15;185(19):3487-3500.e14. doi: 10.1016/j.cell.2022.08.009. Epub 2022 Sep 2.
The supercoiling of bacterial and archaeal flagellar filaments is required for motility. Archaeal flagellar filaments have no homology to their bacterial counterparts and are instead homologs of bacterial type IV pili. How these prokaryotic flagellar filaments, each composed of thousands of copies of identical subunits, can form stable supercoils under torsional stress is a fascinating puzzle for which structural insights have been elusive. Advances in cryoelectron microscopy (cryo-EM) make it now possible to directly visualize the basis for supercoiling, and here, we show the atomic structures of supercoiled bacterial and archaeal flagellar filaments. For the bacterial flagellar filament, we identify 11 distinct protofilament conformations with three broad classes of inter-protomer interface. For the archaeal flagellar filament, 10 protofilaments form a supercoil geometry supported by 10 distinct conformations, with one inter-protomer discontinuity creating a seam inside of the curve. Our results suggest that convergent evolution has yielded stable superhelical geometries that enable microbial locomotion.
细菌和古菌鞭毛丝的超螺旋化对于运动是必需的。古菌鞭毛丝与其细菌对应物没有同源性，而是细菌 IV 型菌毛的同源物。这些由数千个相同亚基组成的原核鞭毛丝如何在扭转力下形成稳定的超螺旋是一个引人入胜的谜题，结构方面的见解一直难以捉摸。冷冻电子显微镜（cryo-EM）的进展使得直接可视化超螺旋的基础成为可能，在这里，我们展示了超螺旋细菌和古菌鞭毛丝的原子结构。对于细菌鞭毛丝，我们确定了 11 种不同的原丝构象，具有三个广泛的亚基间界面类别。对于古菌鞭毛丝，10 个原丝形成一个由 10 种不同构象支撑的超螺旋几何形状，一个亚基间不连续处在曲线内部形成一个接缝。我们的结果表明，趋同进化产生了稳定的超螺旋几何形状，使微生物能够运动。
