Division of Biochemistry and Molecular Biology, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
Dev Cell. 2011 Apr 19;20(4):540-9. doi: 10.1016/j.devcel.2011.02.004.
Septins are GTP-binding proteins that form ordered, rod-like multimeric complexes and polymerize into filaments, but how such supramolecular structure is related to septin function was unclear. In Saccharomyces cerevisiae, four septins form an apolar hetero-octamer (Cdc11-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Cdc11) that associates end-to-end to form filaments. We show that septin filament assembly displays previously unanticipated plasticity. Cells lacking Cdc10 or Cdc11 are able to divide because the now-exposed subunits (Cdc3 or Cdc12, respectively) retain an ability to homodimerize via their so-called G interface, thereby allowing for filament assembly. In such cdc10Δ and cdc11Δ cells, the remaining septins, like wild-type complexes, localize to the cortex at the bud neck and compartmentalize nonseptin factors, consistent with a diffusion barrier composed of continuous filaments in intimate contact with the plasma membrane. Conversely, Cdc10 or Cdc11 mutants that cannot self-associate, but "cap" Cdc3 or Cdc12, respectively, prevent filament formation, block cortical localization, and kill cells.
septins 是一类 GTP 结合蛋白，可形成有序的棒状多聚体复合物并聚合形成纤维，但这种超分子结构如何与 septin 功能相关尚不清楚。在酿酒酵母中，四个 septin 形成非极性异八聚体（Cdc11-Cdc12-Cdc3-Cdc10-Cdc10-Cdc3-Cdc12-Cdc11），该异八聚体首尾相连形成纤维。我们发现 septin 纤维组装表现出以前未预料到的可塑性。由于现在暴露的亚基（分别为 Cdc3 或 Cdc12）通过其所谓的 G 界面保留了同源二聚化的能力，从而允许纤维组装，因此缺失 Cdc10 或 Cdc11 的细胞仍能够分裂。在这些 cdc10Δ 和 cdc11Δ 细胞中，其余 septin 与野生型复合物一样，定位于芽颈处的皮质，并分隔非 septin 因子，与由与质膜紧密接触的连续纤维组成的扩散屏障一致。相反，不能自身组装但分别“帽化”Cdc3 或 Cdc12 的 Cdc10 或 Cdc11 突变体阻止纤维形成、阻断皮质定位并杀死细胞。
