Department of Molecular Biology, Umeå University, SE-901 87 Umeå, Sweden.
Mol Biol Cell. 2011 Sep;22(17):3152-64. doi: 10.1091/mbc.E11-03-0253. Epub 2011 Jul 7.
Septins are conserved GTP-binding proteins that assemble into lateral diffusion barriers and molecular scaffolds. Vertebrate genomes contain 9-17 septin genes that encode both ubiquitous and tissue-specific septins. Expressed septins may assemble in various combinations through both heterotypic and homotypic G-domain interactions. However, little is known regarding assembly states of mammalian septins and mechanisms directing ordered assembly of individual septins into heteromeric units, which is the focus of this study. Our analysis of the septin system in cells lacking or overexpressing selected septins reveals interdependencies coinciding with previously described homology subgroups. Hydrodynamic and single-particle data show that individual septins exist solely in the context of stable six- to eight-subunit core heteromers, all of which contain SEPT2 and SEPT6 subgroup members and SEPT7, while heteromers comprising more than six subunits also contain SEPT9. The combined data suggest a generic model for how the temporal order of septin assembly is homology subgroup-directed, which in turn determines the subunit arrangement of native heteromers. Because mammalian cells normally express multiple members and/or isoforms of some septin subgroups, our data also suggest that only a minor fraction of native heteromers are arranged as perfect palindromes.
septins 是保守的 GTP 结合蛋白，可组装成侧向扩散障碍和分子支架。脊椎动物基因组包含 9-17 个 septin 基因，编码普遍存在和组织特异性的 septin。表达的 septin 可以通过异型和同型 G 结构域相互作用以各种组合组装。然而，关于哺乳动物 septin 的组装状态以及指导单个 septin 有序组装成异源二聚体的机制知之甚少，这是本研究的重点。我们对缺失或过表达选定 septin 的细胞中的 septin 系统进行的分析揭示了与先前描述的同源亚组相吻合的相互依存关系。流体动力学和单颗粒数据表明，单个 septin 仅存在于稳定的六至八亚基核心异源二聚体的环境中，所有这些异源二聚体都包含 SEPT2 和 SEPT6 亚组成员和 SEPT7，而包含超过六个亚基的异源二聚体还包含 SEPT9。综合数据表明，一种通用模型可以解释 septin 组装的时间顺序如何受同源亚组指导，而这反过来又决定了天然异源二聚体的亚基排列。由于哺乳动物细胞通常表达多个成员和/或某些 septin 亚组的同工型，我们的数据还表明，只有一小部分天然异源二聚体排列为完美的回文。
