Furukawa R, Fechheimer M
Department of Cellular Biology, University of Georgia, Athens 30602, USA.
Biochemistry. 1996 Jun 4;35(22):7224-32. doi: 10.1021/bi9601924.
We have studied the formation of bundles in mixtures of actin with the Dictyostelium 30 kDa actin-bundling protein as a function of 30 kDa protein concentration, actin concentration, and filament length. The presence of the 30 kDa protein promotes formation of filament bundles at actin concentrations and filament lengths that are not spontaneously aligned into liquid crystalline domains in the absence of the 30 kDa protein. Bundle formation in the presence of the 30 kDa protein was observed over a broad range of actin filament lengths and concentrations. Bundling was filament length dependent, and short filaments were more efficiently bundled. Bundles formed at actin concentrations as low as 2 microM. The volume fraction of the bundled portion and concentrations of actin and the 30 kDa protein in the bundled portion were measured using a sedimentation assay. Bundles have concentrations of actin and 30 kDa protein that are 10-20 and 5-20 times, respectively, greater than that of the bulk solution. Computer modeling reveals that bundling of actin by a bundling protein increases both the mean length and the polydispersity of the length distribution, factors which lower the actin concentration required for spontaneous alignment within the bundle. We propose that entropy-driven spontaneous ordering may contribute to bundle formation in two ways. Bundling of actin creates longer aggregates with a more polydisperse length distribution in which actin aligns spontaneously within the bundle at very low concentrations. In addition, bundling creates locally high concentrations of actin within these aggregates that will spontaneously align, providing an additional driving force for bundle ordering.
我们研究了肌动蛋白与盘基网柄菌30 kDa肌动蛋白成束蛋白的混合物中束状物的形成，该过程是30 kDa蛋白浓度、肌动蛋白浓度和丝长度的函数。30 kDa蛋白的存在促进了肌动蛋白束的形成，其形成时的肌动蛋白浓度和丝长度在没有30 kDa蛋白时不会自发排列成液晶域。在广泛的肌动蛋白丝长度和浓度范围内，均观察到了30 kDa蛋白存在时的束状物形成。成束作用依赖于丝长度，短丝更易成束。在低至2 microM的肌动蛋白浓度下也能形成束状物。使用沉降分析测量了束状部分的体积分数以及束状部分中肌动蛋白和30 kDa蛋白的浓度。束状物中肌动蛋白和30 kDa蛋白的浓度分别比本体溶液中的浓度高10 - 20倍和5 - 20倍。计算机建模表明，成束蛋白对肌动蛋白的成束作用增加了平均长度和长度分布的多分散性，这些因素降低了束内自发排列所需的肌动蛋白浓度。我们提出，熵驱动的自发排序可能通过两种方式促成束状物的形成。肌动蛋白的成束作用产生了更长的聚集体，其长度分布更具多分散性，其中肌动蛋白在极低浓度下会在束内自发排列。此外，成束作用在这些聚集体中产生了局部高浓度的肌动蛋白，这些肌动蛋白会自发排列，为束状物的有序排列提供了额外的驱动力。
