Suzuki A, Yamazaki M, Ito T
Department of Biophysics, Faculty of Science, Kyoto University, Japan.
Biochemistry. 1989 Jul 25;28(15):6513-8. doi: 10.1021/bi00441a052.
A high molecular weight inert molecule, poly(ethylene glycol) (PEG), or a soluble protein, ovalbumin, causes parallel bundles of actin filaments in a crystalline-like structure under physiological conditions of ionic compositions and pH. The bundle formation depends on the molecular weight of PEG, and a larger molecular weight of PEG can make the bundle at a lower concentration. Actin bundle formation has a discrete dependence on the concentration of PEG. The light scattering following PEG-induced bundle formation increased abruptly at 4.5% (w/w) PEG 6000, while at concentrations less than or equal to 4.0% (w/w) no increase was observed. Labeling actin filaments with heavy meromyosin indicated that the polarity of the filament in the bundle is random. The PEG-induced bundle formation depends on the ionic strength of the solutions and also the concentration of the filament, showing that a higher concentration of PEG was required at lower ionic strength or a lower concentration of the filament. The results described above cannot be explained on the basis of the postulation that the direct binding of PEG molecules to the actin filaments may cause bundle formation. Alternatively, the mechanism can be explained reasonably by the theory of osmoelastic coupling based on preferential exclusion of PEG molecules from the filament surface. High molecular weight molecules such as PEG should be preferentially excluded from the region adjacent to the actin filaments (exclusion layer) by steric hindrance, thereby making imbalance of osmolarity between the bulk and the exclusion layer. This imbalance puts an osmotic stress on the actin filament.(ABSTRACT TRUNCATED AT 250 WORDS)
一种高分子量惰性分子聚乙二醇（PEG）或可溶性蛋白质卵清蛋白，在离子组成和pH值的生理条件下会使肌动蛋白丝形成类似晶体结构的平行束。束的形成取决于PEG的分子量，分子量越大，形成束所需的浓度越低。肌动蛋白束的形成对PEG浓度有离散依赖性。PEG诱导束形成后，在4.5%（w/w）的PEG 6000时，光散射突然增加，而在浓度小于或等于4.0%（w/w）时未观察到增加。用重酶解肌球蛋白标记肌动蛋白丝表明，束中丝的极性是随机的。PEG诱导的束形成取决于溶液的离子强度以及丝的浓度，这表明在较低离子强度或较低丝浓度下需要更高浓度的PEG。上述结果不能基于PEG分子直接与肌动蛋白丝结合可能导致束形成的假设来解释。相反，基于PEG分子从丝表面优先排除的渗透弹性耦合理论可以合理地解释这一机制。像PEG这样的高分子量分子应通过空间位阻优先从与肌动蛋白丝相邻的区域（排除层）排除，从而使本体和排除层之间的渗透压失衡。这种失衡对肌动蛋白丝施加了渗透应力。（摘要截短于250字）
