Department of Biochemistry, University of Washington, Seattle, WA 98195.
Department of Anatomy & Cell Biology, McGill University, Montreal, QC H3A 0C7, Canada.
Proc Natl Acad Sci U S A. 2018 Mar 27;115(13):3356-3361. doi: 10.1073/pnas.1715836115. Epub 2018 Feb 13.
Bacterial actins are an evolutionarily diverse family of ATP-dependent filaments built from protomers with a conserved structural fold. Actin-based segregation systems are encoded on many bacterial plasmids and function to partition plasmids into daughter cells. The bacterial actin AlfA segregates plasmids by a mechanism distinct from other partition systems, dependent on its unique dynamic properties. Here, we report the near-atomic resolution electron cryo-microscopy structure of the AlfA filament, which reveals a strikingly divergent filament architecture resulting from the loss of a subdomain conserved in all other actins and a mode of ATP binding. Its unusual assembly interfaces and nucleotide interactions provide insight into AlfA dynamics, and expand the range of evolutionary variation accessible to actin quaternary structure.
细菌肌动蛋白是一组进化上多样化的 ATP 依赖性纤维，由具有保守结构折叠的原体构成。基于肌动蛋白的分离系统编码在许多细菌质粒上，其功能是将质粒分配到子细胞中。细菌肌动蛋白 AlfA 通过一种与其他分离系统不同的机制来分离质粒，这依赖于其独特的动态特性。在这里，我们报告了 AlfA 纤维的近原子分辨率电子冷冻显微镜结构，该结构揭示了一种惊人的发散纤维结构，这种结构是由于失去了所有其他肌动蛋白中保守的亚结构域以及一种 ATP 结合方式所致。其不寻常的组装界面和核苷酸相互作用提供了对 AlfA 动力学的深入了解，并扩展了肌动蛋白四级结构可获得的进化变异范围。
