Microscopic and semimacroscopic redox calculations: What can and cannot be learned from continuum models

被引:103
作者
Warshel, A [1 ]
Papazyan, A [1 ]
Muegge, I [1 ]
机构
[1] UNIV SO CALIF,DEPT CHEM,LOS ANGELES,CA 90089
来源
JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY | 1997年 / 2卷 / 01期
关键词
redox potentials; proteins; electrostatic effects; continuum models; dielectric constants;
D O I
10.1007/s007750050119
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The major role of electrostatic effects in the control of redox potentials in proteins is now widely appreciated. However, the evaluation and conceptualization of the actual electrostatic contributions is far from trivial, and some models still overlook the nature of electrostatic effects in proteins. This commentary considers different contributions to redox potentials of proteins and discusses the ability of different models to capture these contributions. It is pointed out that macroscopic models which consider the protein as a medium of uniform low dielectric constant cannot reproduce the proper physics of redox proteins. In particular, it is pointed out that the crucial effects of the protein permanent dipoles must be taken into account explicit-ly and that these permanent dipoles involve effective dielectric constants that are different from those for ionized residues. It is also argued that the reorganization of the protein upon change of oxidation states or ionization of protein residues should be taken into account in redox calculations. The role of water penetration and the inadequacy of describing electrostatic effects by solvent accessibility is briefly mentioned. The nature and the meaning of the ''dielectric constant'' that should be used in redox calculations are also discussed. It is pointed out that the ''dielectric constant'' epsilon(p) used in current discretized continuum (DC) models is simply a representation of the contributions which are treated implicitly and not the proper dielectric constant of the protein. It is then explained that the need to use a large ''dielectric constant'' in DC models reflects, among other factors, the implicit representation of the reorganization of permanent dipoles, and that even an explicit treatment of the fluctuations of ionized surface residues will lead to incorrect results when one uses epsilon(p)=<(epsilon)over bar> in continuum treatments. Finally, it is suggested that although the discussion and classification of different contributions to redox potentials is very useful, only the evaluation of the totality of the protein contributions (rather than an arbitrary subset) can lead to a quantitative understanding of redox proteins.
引用
收藏
页码:143 / 152
页数:10
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