Department of Biochemistry and Molecular Biology, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA.
J Mol Biol. 2012 Apr 20;418(1-2):103-16. doi: 10.1016/j.jmb.2012.02.012. Epub 2012 Feb 22.
Actin is a ubiquitous eukaryotic protein that is responsible for cellular scaffolding, motility, and division. The ability of actin to form a helical filament is the driving force behind these cellular activities. Formation of a filament depends on the successful exchange of actin's ADP for ATP. Mammalian profilin is a small actin binding protein that catalyzes the exchange of nucleotide and facilitates the addition of an actin monomer to a growing filament. Here, crystal structures of profilin-actin have been determined to show an actively exchanging ATP. Structural analysis shows how the binding of profilin to the barbed end of actin causes a rotation of the small domain relative to the large domain. This conformational change is propagated to the ATP site and causes a shift in nucleotide loops, which in turn causes a repositioning of Ca(2+) to its canonical position as the cleft closes around ATP. Reversal of the solvent exposure of Trp356 is also involved in cleft closure. In addition, secondary calcium binding sites were identified.
肌动蛋白是一种普遍存在的真核生物蛋白，负责细胞支架、运动和分裂。肌动蛋白形成螺旋丝的能力是这些细胞活动的驱动力。丝的形成取决于肌动蛋白 ADP 成功交换为 ATP。哺乳动物 Profilin 是一种小的肌动蛋白结合蛋白，可催化核苷酸交换并促进肌动蛋白单体添加到生长的丝上。在这里，确定了 Profilin-actin 的晶体结构以显示正在进行交换的 ATP。结构分析表明，Profilin 与肌动蛋白的球状末端结合如何导致小结构域相对于大结构域旋转。这种构象变化传播到 ATP 位点并导致核苷酸环移位，这反过来又导致 Ca(2+)重新定位到其作为裂缝围绕 ATP 关闭的典型位置。Trp356 的溶剂暴露的反转也参与了裂缝的关闭。此外，还确定了次要的钙结合位点。
