Izoré Thierry, van den Ent Fusinita
MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
Subcell Biochem. 2017;84:245-266. doi: 10.1007/978-3-319-53047-5_8.
A diverse set of protein polymers, structurally related to actin filaments contributes to the organization of bacterial cells as cytomotive or cytoskeletal filaments. This chapter describes actin homologs encoded by bacterial chromosomes. MamK filaments, unique to magnetotactic bacteria, help establishing magnetic biological compasses by interacting with magnetosomes. Magnetosomes are intracellular membrane invaginations containing biomineralized crystals of iron oxide that are positioned by MamK along the long-axis of the cell. FtsA is widespread across bacteria and it is one of the earliest components of the divisome to arrive at midcell, where it anchors the cell division machinery to the membrane. FtsA binds directly to FtsZ filaments and to the membrane through its C-terminus. FtsA shows altered domain architecture when compared to the canonical actin fold. FtsA's subdomain 1C replaces subdomain 1B of other members of the actin family and is located on the opposite side of the molecule. Nevertheless, when FtsA assembles into protofilaments, the protofilament structure is preserved, as subdomain 1C replaces subdomain IB of the following subunit in a canonical actin filament. MreB has an essential role in shape-maintenance of most rod-shaped bacteria. Unusually, MreB filaments assemble from two protofilaments in a flat and antiparallel arrangement. This non-polar architecture implies that both MreB filament ends are structurally identical. MreB filaments bind directly to membranes where they interact with both cytosolic and membrane proteins, thereby forming a key component of the elongasome. MreB filaments in cells are short and dynamic, moving around the long axis of rod-shaped cells, sensing curvature of the membrane and being implicated in peptidoglycan synthesis.
一组结构上与肌动蛋白丝相关的多样蛋白质聚合物，作为细胞运动或细胞骨架丝有助于细菌细胞的组织。本章描述了细菌染色体编码的肌动蛋白同源物。趋磁细菌特有的MamK丝通过与磁小体相互作用帮助建立磁性生物罗盘。磁小体是包含生物矿化氧化铁晶体的细胞内膜内陷，由MamK沿着细胞的长轴定位。FtsA广泛存在于细菌中，是最早到达细胞中部的分裂体成分之一，在那里它将细胞分裂机器锚定到膜上。FtsA通过其C末端直接结合FtsZ丝和膜。与典型的肌动蛋白折叠相比，FtsA显示出改变的结构域结构。FtsA的亚结构域1C取代了肌动蛋白家族其他成员的亚结构域1B，位于分子的另一侧。然而，当FtsA组装成原丝时，原丝结构得以保留，因为亚结构域1C取代了典型肌动蛋白丝中后续亚基的亚结构域1B。MreB在大多数杆状细菌的形状维持中起重要作用。不同寻常的是，MreB丝由两条原丝以扁平且反平行的排列组装而成。这种非极性结构意味着MreB丝的两端在结构上是相同的。MreB丝直接结合到膜上，在那里它们与胞质和膜蛋白相互作用，从而形成伸长体的关键成分。细胞中的MreB丝短且动态，围绕杆状细胞的长轴移动，感知膜的曲率并参与肽聚糖合成。
