Ligand Loop Effects on the Free Energy Change of Redox and pH-Dependent Equilibria in Cupredoxins Probed on Amicyanin Variants
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- 作者：Gianantonio Battistuzzi ; Marco Borsari ; Gerard W. Canters ; Giulia di Rocco ; Ellen de Waal ; Yvonne Arendsen ; Alan Leonardi ; Antonio Ranieri ; and Marco Sola
- 刊名：Biochemistry
- 出版年：2005
- 出版时间：July 26, 2005
- 年：2005
- 卷：44
- 期：29
- 页码：9944 - 9949
- 全文大小：70K
- 年卷期：v.44,no.29(July 26, 2005)
- ISSN：1520-4995
文摘
In this work, we have determined the thermodynamic parameters of the reduction of fourdifferent variants of Thiobacillus versutus amicyanin by electrochemical techniques. In addition, thethermodynamic parameters were determined of the low-pH conformational change involving protonationof the C-terminal histidine ligand and the concomitant dissociation of this histidine from the Cu(I) ion.In these variants, the native C-terminal loop containing the Cys, His, and Met copper ligands has beenreplaced with the corresponding polypeptide segments of Pseudomonas aeruginosa azurin, Populus nigraplastocyanin, Alcaligenes faecalis S-6 pseudoazurin, and Thiobacillus ferrooxidans rusticyanin. For thereduction reaction, each loop invariably holds an entropic "memory" of the mother protein. Thethermodynamics of the low-pH transition vary in a fashion that is species-dependent. When present, thememory effect again shows a large entropic component. In particular, loop elongation tends to favor theformation of the Cu(I)-His bond (hence disfavors His protonation, yielding lower pKa values) probablydue to an increased flexibility of the loop in the reduced state. Overall, it appears that both reduction andlow-pH transition are loop-responsive processes. The spacing between the ligands mostly affects the changein the conformational freedom that accompanies the reaction.