Department of Biochemistry and Biophysics, Oregon State University, Corvallis, Oregon 97331, USA.
J Biol Chem. 2009 Nov 27;284(48):33115-21. doi: 10.1074/jbc.M109.048587. Epub 2009 Sep 16.
Dynein light chains are thought to increase binding efficiency of dynein intermediate chain to both dynein heavy chain and dynactin, but their exact role is not clear. Isothermal titration calorimetry and x-ray crystallography reported herein indicate that multivalency effects underlie efficient dynein assembly and regulation. For a ternary complex of a 60-amino acid segment of dynein intermediate chain (IC) bound to two homodimeric dynein light chains Tctex1 and LC8, there is a 50-fold affinity enhancement for the second light chain binding. For a designed IC construct containing two LC8 sites, observed the 1000-fold enhancement reflects a remarkably pure entropic chelate effect of a magnitude commensurate with theoretical predictions. The lower enhancement in wild-type IC is attributed to unfavorable free energy changes associated with incremental interactions of IC with Tctex1. Our results show assembled dynein IC as an elongated, flexible polybivalent duplex, and suggest that polybivalency is an important general mechanism for constructing stable yet reversible and functionally versatile complexes.
动力蛋白轻链被认为可以提高动力蛋白中间链与动力蛋白重链和动力蛋白激活蛋白之间的结合效率，但它们的确切作用尚不清楚。本文报道的等温热滴定法和 X 射线晶体学表明，多价效应是动力蛋白有效组装和调节的基础。对于与两个同源二聚体动力蛋白轻链 Tctex1 和 LC8 结合的动力蛋白中间链 (IC) 的 60 个氨基酸片段的三元复合物，第二个轻链的结合亲和力增强了 50 倍。对于含有两个 LC8 位点的设计 IC 结构，观察到的 1000 倍增强反映了一个显著的纯熵螯合效应，其大小与理论预测相符。野生型 IC 中较低的增强归因于与 IC 与 Tctex1 的增量相互作用相关的不利自由能变化。我们的结果表明组装的动力蛋白 IC 是一个长而灵活的多价双链体，并表明多价性是构建稳定但可还原且功能多样的复合物的重要一般机制。
