Inactive conformation enhances binding function in physiological conditions.
Inactive conformation enhances binding function in physiological conditions.
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非活性构象增强了生理条件下的结合功能。
DOI：
10.1073/pnas.1503160112
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发表时间：
2015
影响因子：
11.1
通讯作者：
Thomas,WendyE
中科院分区：
文献类型：
--
作者：
Yakovenko,Olga;Tchesnokova,Veronika;Sokurenko,EvgeniV;Thomas,WendyE
许多受体表现出构象灵活性，其中结合口袋在没有配体的情况下具有开放的非活性构象，而当与配体结合时具有紧密的活性构象。在这里，我们研究细菌粘附素FimH，以通过比较两种变体来解决口袋的非活性构象在启动结合中的作用：野生型FimH变体，当不与其目标甘露糖结合时处于非活性状态，以及工程激活变体，始终处于活性状态。毫不奇怪，活化的FimH具有更长的寿命和更高的亲和力，并且表达活化的FimH的细菌在静态条件下结合得更好。然而，表达野生型FimH的细菌在流动中结合得更好。野生型和激活的FimH表现出相似的机械强度，这可能是因为机械力诱导了野生型FimH的激活状态。然而，野生型FimH显示出比激活的FimH更快的键缔合速率。此外，不同的FimH变异体在流动中介导黏附的能力反映了处于非活性状态的FimH的比例。这些结果证明了一种新的与配体相关的构象变化模型，我们称之为动力学选择模型，在该模型中，配体结合选择更快结合的非活性状态，然后诱导活性状态。该模型预测，在细胞黏附的生理条件下，机械力将驱动一个非平衡循环，该循环利用非活跃状态的快速结合率和活跃状态的缓慢解结率，以获得比平衡状态可能的更高的有效亲和力。
Many receptors display conformational flexibility, in which the binding pocket has an open inactive conformation in the absence of ligand and a tight active conformation when bound to ligand. Here we study the bacterial adhesin FimH to address the role of the inactive conformation of the pocket for initiating binding by comparing two variants: a wild-type FimH variant that is in the inactive state when not bound to its target mannose, and an engineered activated variant that is always in the active state. Not surprisingly, activated FimH has a longer lifetime and higher affinity, and bacteria expressing activated FimH bound better in static conditions. However, bacteria expressing wild-type FimH bound better in flow. Wild-type and activated FimH demonstrated similar mechanical strength, likely because mechanical force induces the active state in wild-type FimH. However, wild-type FimH displayed a faster bond association rate than activated FimH. Moreover, the ability of different FimH variants to mediate adhesion in flow reflected the fraction of FimH in the inactive state. These results demonstrate a new model for ligand-associated conformational changes that we call the kinetic-selection model, in which ligand-binding selects the faster-binding inactive state and then induces the active state. This model predicts that in physiological conditions for cell adhesion, mechanical force will drive a nonequilibrium cycle that uses the fast binding rate of the inactive state and slow unbinding rate of the active state, for a higher effective affinity than is possible at equilibrium.