Department of Chemistry, University of Minnesota, Minneapolis, MN, 55455, USA.
Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN, 55455, USA.
Nat Commun. 2019 Feb 18;10(1):799. doi: 10.1038/s41467-019-08655-7.
Enzymes accelerate the rate of chemical transformations by reducing the activation barriers of uncatalyzed reactions. For signaling enzymes, substrate recognition, binding, and product release are often rate-determining steps in which enthalpy-entropy compensation plays a crucial role. While the nature of enthalpic interactions can be inferred from structural data, the molecular origin and role of entropy in enzyme catalysis remains poorly understood. Using thermocalorimetry, NMR, and MD simulations, we studied the conformational landscape of the catalytic subunit of cAMP-dependent protein kinase A, a ubiquitous phosphoryl transferase involved in a myriad of cellular processes. Along the enzymatic cycle, the kinase exhibits positive and negative cooperativity for substrate and nucleotide binding and product release. We found that globally coordinated changes of conformational entropy activated by ligand binding, together with synchronous and asynchronous breathing motions of the enzyme, underlie allosteric cooperativity along the kinase's cycle.
酶通过降低无催化剂反应的活化能垒来加速化学反应的速率。对于信号酶，底物识别、结合和产物释放通常是速率决定步骤，其中焓熵补偿起着关键作用。虽然可以从结构数据推断出焓相互作用的性质，但酶催化中熵的分子起源和作用仍知之甚少。本研究使用量热法、NMR 和 MD 模拟研究了 cAMP 依赖性蛋白激酶 A 催化亚基的构象景观，该蛋白激酶 A 是一种普遍存在的磷酸转移酶，参与多种细胞过程。在酶循环过程中，激酶对底物和核苷酸结合以及产物释放表现出正协同性和负协同性。我们发现，配体结合激活的构象熵的整体协调变化，以及酶的同步和异步呼吸运动，是激酶循环中变构协同作用的基础。
