Redox thermodynamics of blue copper proteins
Redox thermodynamics of blue copper proteins
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DOI：
10.1021/ja982126q
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发表时间：
1999-01-27
影响因子：
15
通讯作者：
Sola, M
中科院分区：
文献类型：
--
作者：
Battistuzzi, G;Borsari, M;Sola, M
蛋白质还原的热力学参数在中性pH下，通过伏安技术在非等温实验中测量了许多蓝铜蛋白的Δ H度（rc）和Δ S度（rc），所述蓝铜蛋白包括菠菜质体蓝蛋白、黄瓜质体蓝蛋白、铜绿假单胞菌天青蛋白、漆树星花青蛋白、黄瓜星花青蛋白和辣根花青蛋白。本文讨论了十二种不同来源的蓝铜蛋白的电子交换反应的热力学。在这类蛋白质中，还原项（-Δ H度（rc）/F）是对还原电位的主要贡献。然而，熵项（T Δ S度（rc）/F）严重影响E度，特别是对于天青。这些数据进行了分析，在光的结构和动力学信息的蛋白质折叠，几何和电子功能的铜连接，和溶剂化性质的两个氧化还原状态。可以清楚地看出，与其他铜氧还蛋白相比，“植蓝蛋白”亚家族的还原焓是负的，这很可能是由于铜离子的更强的轴向连接（这导致近四面体配位几何形状）和该位点对溶剂的更大暴露，这两者都是稳定Cu（II）离子的因素。还原熵，在大多数情况下是负的，而显然是与网站的救赎性质。此外，通过与I类细胞色素c类比，蛋白质刚性的增加也可能有助于还原时的熵损失。最后，通过对高电位电子转移金属蛋白还原热力学的研究，发现蛋白质控制策略对高电位电子转移金属蛋白的还原热力学具有重要意义（蓝铜蛋白，I类细胞色素c，HiPIP）是相同的：金属/蛋白质界面上配体结合相互作用和静电因素产生的主导焓项，强烈稳定还原态，由于蛋白质动力学和拯救性质的变化，最常与较弱的熵项相反，这不利于蛋白质减少。
The thermodynamic parameters of protein reduction (Delta H degrees'(rc) and Delta S degrees'(rc)) were measured for a number of blue copper proteins including spinach plastocyanin, cucumber plastocyanin, Pseudomonas aeruginosa azurin, Rhus vernicifera stellacyanin, cucumber stellacyanin, and horseradish umecyanin through voltammetric techniques in nonisothermal experiments at neutral pH. Including previous estimates for other members of the same protein family, we discuss here the thermodynamics of the electron-exchange reaction for twelve blue copper proteins from different sources. The enthalpic term (-Delta H degrees'(rc)/F) turns out to be the dominant contribution to the reduction potential in this protein class. However, the entropic term (T Delta S degrees'(rc)/F) heavily affects E degrees', especially for the azurins. These data were analyzed in the light of the structural and dynamic information available on protein folding, geometric and electronic features of copper ligation, and solvation properties of the two redox states. It is clearly seen that the reduction enthalpy of the subfamily of the "phytocyanins" is less negative as compared to that of the other cupredoxins, most likely owing to a stronger axial ligation of the copper ion (which results in a nearly tetrahedral coordination geometry) and the greater exposition of the site to the solvent, which are both factors that stabilize the Cu(II) ion. The reduction entropy, which in most cases is negative, is instead apparently related to the salvation properties of the site. In addition, by analogy with class I cytochromes c, an increase in protein rigidity could also contribute to the entropy loss on reduction. Finally, it is apparent that the strategy of protein control of the reduction thermodynamics in high-potential electron-transfer metalloproteins (blue copper proteins, class I cytochromes c, HiPIPs) is the same: a dominant enthalpic term arising from ligand-binding interactions and electrostatic factors at the metal/protein interface, which strongly stabilizes the reduced state, is most often opposed by a weaker entropic term due to changes in protein dynamics and salvation properties, which disfavors protein reduction.