Septins are GTP binding proteins considered to be novel components of the cytoskeleton. They polymerize into filaments based on hexameric or octameric core particles in which two copies of either three or four different septins, respectively, assemble into a specific sequence. Viable combinations of the 13 human septins are believed to obey substitution rules in which the different septins involved must come from distinct subgroups. The hexameric assembly, for example, has been reported to be SEPT7–SEPT6–SEPT2–SEPT2–SEPT6–SEPT7. Here, we have replaced SEPT2 by SEPT5 according to the substitution rules and used transmission electron microscopy to demonstrate that the resulting recombinant complex assembles into hexameric particles which are inverted with respect that predicted previously. MBP‐SEPT5 constructs and immunostaining show that SEPT5 occupies the terminal positions of the hexamer. We further show that this is also true for the assembly including SEPT2, in direct contradiction with that reported previously. Consequently, both complexes expose an NC interface, as reported for yeast, which we show to be more susceptible to high salt concentrations. The correct assembly for the canonical combination of septins 2‐6‐7 is therefore established to be SEPT2–SEPT6–SEPT7–SEPT7–SEPT6–SEPT2, implying the need for revision of the mechanisms involved in filament assembly.

中文翻译：

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哺乳动物septin复合物中亚基的修订顺序。

Septins是GTP结合蛋白，被认为是细胞骨架的新组成部分。它们聚合成基于六聚体或八聚体核心颗粒的长丝，其中两个或三个或四个不同septin的两个副本分别组装成特定的序列。据信13种人类Septin的可行组合遵循替代规则，其中涉及的不同Septin必须来自不同的亚组。例如，据报道该六聚体为SEPT7–SEPT6–SEPT2–SEPT2–SEPT6–SEPT7。在这里，我们已根据替换规则将SEPT2替换为SEPT5，并使用透射电子显微镜证明了所产生的重组复合物组装成六聚体颗粒，相对于先前的预测，该六聚体颗粒是反向的。MBP-SEPT5构建体和免疫染色表明SEPT5占据六聚体的末端位置。我们进一步表明，对于包括SEPT2在内的程序集也是如此，与先前报道的直接矛盾。因此，正如针对酵母报道的那样，两种复合物都暴露出一个NC界面，我们证明它对高盐浓度更敏感。因此，确定针对Septins 2-6-7的规范组合的正确组装为SEPT2–SEPT6–SEPT7–SEPT7–SEPT6–SEPT2，这意味着需要修改与细丝组装有关的机制。我们证明它更容易受到高盐浓度的影响。因此，确定针对Septins 2-6-7的规范组合的正确组装为SEPT2–SEPT6–SEPT7–SEPT7–SEPT6–SEPT2，这意味着需要修改与细丝组装有关的机制。我们证明它更容易受到高盐浓度的影响。因此，确定针对Septins 2-6-7的规范组合的正确组装为SEPT2–SEPT6–SEPT7–SEPT7–SEPT6–SEPT2，这意味着需要修改与细丝组装有关的机制。