Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St. Louis, MO 63104, USA.
Biochemistry. 2012 Jul 31;51(30):5894-902. doi: 10.1021/bi3006913. Epub 2012 Jul 16.
For almost five decades, two competing mechanisms of ligand recognition, conformational selection and induced fit, have dominated our interpretation of ligand binding in biological macromolecules. When binding-dissociation events are fast compared to conformational transitions, the rate of approach to equilibrium, k(obs), becomes diagnostic of conformational selection or induced fit based on whether it decreases or increases, respectively, with the ligand concentration, [L]. However, this simple conclusion based on the rapid equilibrium approximation is not valid in general. Here we show that conformational selection is associated with a rich repertoire of kinetic properties, with k(obs) decreasing or increasing with [L] depending on the relative magnitude of the rate of ligand dissociation, k(off), and the rate of conformational isomerization, k(r). We prove that, even for the simplest two-step mechanism of ligand binding, a decrease in k(obs) with [L] is unequivocal evidence of conformational selection, but an increase in k(obs) with [L] is not unequivocal evidence of induced fit. Ligand binding to glucokinase, thrombin, and its precursor prethrombin-2 are used as relevant examples. We conclude that conformational selection as a mechanism for a ligand binding to its target may be far more common than currently believed.
近五十年来，两种竞争性的配体识别机制，构象选择和诱导契合，主导了我们对生物大分子中配体结合的解释。当结合-解离事件与构象转变相比很快时，达到平衡的速率 k(obs)，根据它是否分别随着配体浓度 [L] 的增加而减小或增加，成为构象选择或诱导契合的诊断依据。然而，这种基于快速平衡近似的简单结论通常并不成立。在这里，我们表明构象选择与丰富的动力学性质相关联，k(obs)随着 [L] 的增加而减小或增加取决于配体解离速率 k(off)和构象异构化速率 k(r)的相对大小。我们证明，即使对于最简单的两步配体结合机制，k(obs)随着 [L] 的减小是构象选择的明确证据，但 k(obs)随着 [L] 的增加并不明确是诱导契合的证据。我们使用葡萄糖激酶、凝血酶及其前体前凝血酶-2 的配体结合作为相关示例。我们的结论是，构象选择作为配体与其靶标结合的机制可能比目前认为的更为普遍。
