肌动蛋白存在于几乎所有真核细胞中，其形式有两种：细丝状F-肌动蛋白，它们驱动包括细胞运动和肌肉收缩在内的很多细胞过程；以及它们由之而产生的单体，即球形或G-肌动蛋白。在G-肌动蛋白向F-肌动蛋白转变的过程中所发生的结构变化仍然不清楚，因为以前关于聚合物的模型一直在很大程度上以G-肌动蛋白的结构为依据。
现在，F-肌动蛋白的结构已以高分辨被确定。该结构显示，两个主要区域（它们在G-肌动蛋白中形成一个推进器一样的缠绕结构）没有缠绕在一起，该分子在F-肌动蛋白中是平坦的。平坦结构与螺旋形排列相结合，可稳定链内和链间的接触。从G到F的构形变化与以前关于肌动蛋白的生物化学研究完全一致。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 457, 441-445 (22 January 2008) | doi:10.1038/nature07685
The nature of the globular- to fibrous-actin transition
Toshiro Oda1,2, Mitsusada Iwasa2, Tomoki Aihara1, Yuichiro Maéda2,3 & Akihiro Narita3
1 X-ray Structural Analysis Research Team, RIKEN SPring-8 Center, RIKEN Harima Institute, 1-1-1, Kouto, Sayo, Hyogo 679-5148, Japan
2 ERATO project 'Actin-filament dynamics', Japan Science and Technology Agency (JST), 1-1-1, Kouto, Sayo, Hyogo 679-5148, Japan
3 Structural Biology Research Center and Division of Biological Science, Graduate School of Science, Nagoya University, Furo, Nagoya 464-8601, Japan
Actin plays crucial parts in cell motility through a dynamic process driven by polymerization and depolymerization, that is, the globular (G) to fibrous (F) actin transition. Although our knowledge about the actin-based cellular functions and the molecules that regulate the G- to F-actin transition is growing, the structural aspects of the transition remain enigmatic. We created a model of F-actin using X-ray fibre diffraction intensities obtained from well oriented sols of rabbit skeletal muscle F-actin to 3.3 ? in the radial direction and 5.6 ? along the equator. Here we show that the G- to F-actin conformational transition is a simple relative rotation of the two major domains by about 20 degrees. As a result of the domain rotation, the actin molecule in the filament is flat. The flat form is essential for the formation of stable, helical F-actin. Our F-actin structure model provides the basis for understanding actin polymerization as well as its molecular interactions with actin-binding proteins.
