van den Ent Fusinita, Møller-Jensen Jakob, Amos Linda A, Gerdes Kenn, Löwe Jan
MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK.
EMBO J. 2002 Dec 16;21(24):6935-43. doi: 10.1093/emboj/cdf672.
It was the general belief that DNA partitioning in prokaryotes is independent of a cytoskeletal structure, which in eukaryotic cells is indispensable for DNA segregation. Recently, however, immunofluorescence microscopy revealed highly dynamic, filamentous structures along the longitudinal axis of Escherichia coli formed by ParM, a plasmid-encoded protein required for accurate segregation of low-copy-number plasmid R1. We show here that ParM polymerizes into double helical protofilaments with a longitudinal repeat similar to filamentous actin (F-actin) and MreB filaments that maintain the cell shape of non-spherical bacteria. The crystal structure of ParM with and without ADP demonstrates that it is a member of the actin family of proteins and shows a domain movement of 25 degrees upon nucleotide binding. Furthermore, the crystal structure of ParM reveals major differences in the protofilament interface compared with F-actin, despite the similar arrangement of the subunits within the filaments. Thus, there is now evidence for cytoskeletal structures, formed by actin-like filaments that are involved in plasmid partitioning in E.coli.
人们普遍认为，原核生物中的DNA分配独立于细胞骨架结构，而在真核细胞中，细胞骨架结构对于DNA分离是必不可少的。然而，最近免疫荧光显微镜显示，沿着大肠杆菌纵轴存在高度动态的丝状结构，这些结构由ParM形成，ParM是一种质粒编码蛋白，对于低拷贝数质粒R1的精确分离是必需的。我们在此表明，ParM聚合成双螺旋原丝，其纵向重复类似于维持非球形细菌细胞形状的丝状肌动蛋白（F-肌动蛋白）和MreB丝。结合和未结合ADP的ParM晶体结构表明，它是肌动蛋白家族蛋白的一员，并且在核苷酸结合后显示出25度的结构域运动。此外，尽管原丝内亚基的排列相似，但ParM的晶体结构显示与F-肌动蛋白相比，原丝界面存在重大差异。因此，现在有证据表明，由肌动蛋白样丝形成的细胞骨架结构参与了大肠杆菌中的质粒分配。
