Mapping Heat Exchange in an Allosteric Protein
Mapping Heat Exchange in an Allosteric Protein
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DOI：
10.1016/j.bpj.2010.12.3739
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发表时间：
2011-02-16
影响因子：
3.4
通讯作者：
Auerbach, Anthony
中科院分区：
文献类型：
--
作者：
Gupta, Shaweta;Auerbach, Anthony
烟碱乙酰胆碱受体（AChR）是突触离子通道，其自发异构化（即，门）之间的休息和积极的构象。我们使用单分子电生理学来测量小鼠神经肌肉AChR门控速率和平衡常数的温度依赖性。从这些，我们估计自由能，焓，和熵的变化所造成的突变的氨基酸位于之间的发射器结合位点和中间的膜域。平衡焓变的范围（13.4 kcal/mol）大于自由能变化的范围（25 ℃时为5.5 kcal/mol）。对于两个残基，速率平衡自由能关系（Φ）的斜率随温度的变化近似恒定。突变体循环分析表明，自由能和自由能都是能量独立突变的加性。我们假设，与结构变化相关的能量变化主要发生在突变位点附近，因此，有可能在AChR门控异构化中进行热交换的残基-残基图。焓变化的结构相关性进行了讨论的蛋白质中的12个不同的突变。
Nicotinic acetylcholine receptors (AChRs) are synaptic ion channels that spontaneously isomerize (i.e., gate) between resting and active conformations. We used single-molecule electrophysiology to measure the temperature dependencies of mouse neuromuscular AChR gating rate and equilibrium constants. From these we estimated free energy, enthalpy, and entropy changes caused by mutations of amino acids located between the transmitter binding sites and the middle of the membrane domain. The range of equilibrium enthalpy change (13.4 kcal/mol) was larger than for free energy change (5.5 kcal/mol at 25 degrees C). For two residues, the slope of the rate-equilibrium free energy relationship (Phi) was approximately constant with temperature. Mutant cycle analysis showed that both free energies and enthalpies are additive for energetically independent mutations. We hypothesize that changes in energy associated with changes in structure mainly occur close to the site of the mutation, and, hence, that it is possible to make a residue-by-residue map of heat exchange in the AChR gating isomerization. The structural correlates of enthalpy changes are discussed for 12 different mutations in the protein.