Steinmetz M O, Hoenger A, Stoffler D, Noegel A A, Aebi U, Schoenenberger C A
M.E. Müller Institute for Structural Biology, University of Basel, Klingelbergstrasse 70, Biozentrum, CH-4056, Basel, Switzerland.
J Mol Biol. 2000 Oct 20;303(2):171-84. doi: 10.1006/jmbi.2000.4129.
To assess more systematically functional differences among non-muscle and muscle actins and the effect of specific mutations on their function, we compared actin from Dictyostelium discoideum (D-actin) with actin from rabbit skeletal muscle (R-actin) with respect to the formation of filaments, their three-dimensional structure and mechanical properties. With Mg(2+) occupying the single high-affinity divalent cation-binding site, the course of polymerization is very similar for the two types of actin. In contrast, when Ca(2+ )is bound, D-actin exhibits a significantly longer lag phase at the onset of polymerization than R-actin. Crossover spacing and helical screw angle of negatively stained filaments are similar for D and R-F-actin filaments, irrespective of the tightly bound divalent cation. However, three-dimensional helical reconstructions reveal that the intersubunit contacts along the two long-pitch helical strands of D-(Ca)F-actin filaments are more tenuous compared to those in R-(Ca)F-actin filaments. D-(Mg)F-actin filaments on the other hand exhibit more massive contacts between the two long-pitch helical strands than R-(Mg)F-actin filaments. Moreover, in contrast to the structure of R-F-actin filaments which is not significantly modulated by the divalent cation, the intersubunit contacts both along and between the two long-pitch helical strands are weaker in D-(Ca)F-actin compared to D-(Mg)F-actin filaments. Consistent with these structural differences, D-(Ca)F-actin filaments were significantly more flexible than D-(Mg)F-actin. Taken together, this work documents that despite being highly conserved, muscle and non-muscle actins exhibit subtle differences in terms of their polymerization behavior, and the three-dimensional structure and mechanical properties of their F-actin filaments which, in turn, may account for their functional diversity.
为了更系统地评估非肌肉肌动蛋白和肌肉肌动蛋白之间的功能差异以及特定突变对其功能的影响，我们比较了盘基网柄菌肌动蛋白（D-肌动蛋白）和兔骨骼肌肌动蛋白（R-肌动蛋白）在细丝形成、三维结构和力学性能方面的差异。当Mg(2+)占据单个高亲和力二价阳离子结合位点时，两种肌动蛋白的聚合过程非常相似。相比之下，当结合Ca(2+)时，D-肌动蛋白在聚合开始时的滞后阶段明显比R-肌动蛋白长。无论紧密结合的二价阳离子如何，D型和R型F-肌动蛋白细丝的负染细丝的交叉间距和螺旋螺角相似。然而，三维螺旋重建显示，与R-(Ca)F-肌动蛋白细丝相比，D-(Ca)F-肌动蛋白细丝沿两条长间距螺旋链的亚基间接触更脆弱。另一方面，D-(Mg)F-肌动蛋白细丝在两条长间距螺旋链之间表现出比R-(Mg)F-肌动蛋白细丝更多的大量接触。此外，与R-F-肌动蛋白细丝的结构不受二价阳离子显著调节相反，与D-(Mg)F-肌动蛋白细丝相比，D-(Ca)F-肌动蛋白沿两条长间距螺旋链以及链之间的亚基间接触较弱。与这些结构差异一致，D-(Ca)F-肌动蛋白细丝比D-(Mg)F-肌动蛋白细丝明显更柔韧。综上所述，这项工作证明，尽管肌肉和非肌肉肌动蛋白高度保守，但它们在聚合行为、F-肌动蛋白细丝的三维结构和力学性能方面表现出细微差异，这些差异反过来可能解释了它们的功能多样性。
