肌動蛋白存在於幾乎所有真核細胞中，其形式有兩種：細絲狀F-肌動蛋白，它們驅動包括細胞運動和肌肉收縮在內的很多細胞過程；以及它們由之而產生的單體，即球形或G-肌動蛋白。在G-肌動蛋白向F-肌動蛋白轉變的過程中所發生的結構變化仍然不清楚，因為以前關於聚合物的模型一直在很大程度上以G-肌動蛋白的結構為依據。
現在，F-肌動蛋白的結構已以高分辨被確定。該結構顯示，兩個主要區域（它們在G-肌動蛋白中形成一個推進器一樣的纏繞結構）沒有纏繞在一起，該分子在F-肌動蛋白中是平坦的。平坦結構與螺旋形排列相結合，可穩定鏈內和鏈間的接觸。從G到F的構形變化與以前關於肌動蛋白的生物化學研究完全一致。（生物谷Bioon.com）
生物谷推薦原始出處：
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.