Mitchison T J
Department of Pharmacology, U.C.S.F. 94143-0450, USA.
Philos Trans R Soc Lond B Biol Sci. 1995 Sep 29;349(1329):299-304. doi: 10.1098/rstb.1995.0117.
Actin filaments and microtubules form the cytoskeleton of all eukaryotic cells, and they are responsible for organizing the cytoplasm and supporting motile processes. Both polymers are highly dynamic, and their polymerization dynamics are central to their organization. Though their evolutionary origins appear to be distinct, actin and tubulin have a similar mechanism for promoting polymerization dynamics in which the energy of nucleotide triphosphate hydrolysis during polymerization is used to weaken the bonds between subunits, thus promoting subsequent depolymerization. The evolutionary origins of actin and tubulin are unclear. It is likely that motile mechanisms driven by reversible polymerization, termed thermal ratchets, are older than those based on ATPase motor proteins. Such mechanisms are still important in modern eukaryotes, and may have powered early versions of the critical motile processes of phagocytosis and chromosome segregation in primitive cells. Thus evolution of dynamic cytoskeletal polymers may have been one of the earliest and most important steps leading to the evolution of eukaryotes. Plausible evolutionary pathways can be constructed leading from simple enzymes to dynamic cytoskeletal polymers.
肌动蛋白丝和微管构成了所有真核细胞的细胞骨架，它们负责组织细胞质并支持运动过程。这两种聚合物都具有高度动态性，其聚合动力学是它们组织方式的核心。尽管它们的进化起源似乎不同，但肌动蛋白和微管蛋白具有相似的促进聚合动力学的机制，其中聚合过程中三磷酸核苷酸水解的能量用于削弱亚基之间的键，从而促进随后的解聚。肌动蛋白和微管蛋白的进化起源尚不清楚。由可逆聚合驱动的运动机制，称为热棘轮，可能比基于ATP酶运动蛋白的机制更古老。这种机制在现代真核生物中仍然很重要，并且可能为原始细胞中吞噬作用和染色体分离等关键运动过程的早期版本提供动力。因此，动态细胞骨架聚合物的进化可能是导致真核生物进化的最早和最重要的步骤之一。可以构建从简单酶到动态细胞骨架聚合物的合理进化途径。
