Derry W B, Wilson L, Jordan M A
Division of Molecular, Cellular, Department of Biological Sciences, University of California, Santa Barbara 93106.
Biochemistry. 1995 Feb 21;34(7):2203-11. doi: 10.1021/bi00007a014.
We have measured the effects of taxol (10 nM to 1 microM) on the growing and shortening dynamics at the ends of individual bovine brain microtubules in vitro and have correlated the effects both with the stoichiometry of taxol binding to tubulin in microtubules and with the changes in the microtubule polymer mass. The results indicate that taxol suppresses microtubule dynamic instability differently depending upon the stoichiometry of taxol binding to the microtubules. At the lowest effective concentrations (< or = 100 nM), substoichiometric binding of taxol to tubulin in microtubules (between 0.001 and 0.01 mol of bound taxol/mol of tubulin in microtubules) potently and selectively suppresses the rate and extent of shortening at plus ends in association with some increase (28% to 60%) in the mass of microtubule polymer. At intermediate taxol concentrations (between 100 nM and 1 microM), the binding of additional taxol molecules to the microtubules (between 0.01 and 0.1 mol of taxol bound/mol of tubulin in microtubules) inhibits both growing and shortening events at both microtubule ends with no additional increase in microtubule polymer mass. At high taxol concentrations and high taxol binding stoichiometries (> or = 1 microM taxol and > or = 0.1 mol of taxol bound/mol of tubulin in microtubules), microtubule mass increases sharply and dynamics is almost completely suppressed. The data support the hypothesis that binding of a molecule of taxol to a tubulin subunit in microtubules induces a conformational change in that subunit that strongly reduces its ability to dissociate when the subunit becomes exposed at the microtubule end.
我们已在体外测量了紫杉醇（10 nM至1 microM）对单个牛脑微管末端生长和缩短动力学的影响，并将这些影响与紫杉醇在微管中与微管蛋白结合的化学计量以及微管聚合物质量的变化相关联。结果表明，根据紫杉醇与微管结合的化学计量，紫杉醇对微管动态不稳定性的抑制作用有所不同。在最低有效浓度（≤100 nM）下，微管中紫杉醇与微管蛋白的亚化学计量结合（微管中每摩尔微管蛋白结合0.001至0.01摩尔结合的紫杉醇）有力且选择性地抑制了正端的缩短速率和程度，同时微管聚合物质量有所增加（28%至60%）。在中等紫杉醇浓度（100 nM至1 microM之间）下，额外的紫杉醇分子与微管结合（微管中每摩尔微管蛋白结合0.01至0.1摩尔紫杉醇）会抑制微管两端的生长和缩短事件，而微管聚合物质量没有进一步增加。在高紫杉醇浓度和高紫杉醇结合化学计量（≥1 microM紫杉醇且微管中每摩尔微管蛋白结合≥0.1摩尔紫杉醇）下，微管质量急剧增加，动力学几乎完全受到抑制。这些数据支持了这样一种假设，即微管中一个紫杉醇分子与一个微管蛋白亚基的结合会诱导该亚基的构象变化，当该亚基在微管末端暴露时，会强烈降低其解离能力。
