Baymann Frauke, Schoepp-Cothenet Barbara, Duval Simon, Guiral Marianne, Brugna Myriam, Baffert Carole, Russell Michael J, Nitschke Wolfgang
CNRS, BIP, UMR 7281, IMM FR3479, Aix-Marseille University, Marseille, France.
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
Front Microbiol. 2018 Jul 3;9:1357. doi: 10.3389/fmicb.2018.01357. eCollection 2018.
Electron bifurcation is here described as a special case of the continuum of electron transfer reactions accessible to two-electron redox compounds with redox cooperativity. We argue that electron bifurcation is foremost an electrochemical phenomenon based on (a) strongly inverted redox potentials of the individual redox transitions, (b) a high endergonicity of the first redox transition, and (c) an escapement-type mechanism rendering completion of the first electron transfer contingent on occurrence of the second one. This mechanism is proposed to govern both the traditional quinone-based and the newly discovered flavin-based versions of electron bifurcation. Conserved and variable aspects of the spatial arrangement of electron transfer partners in flavoenzymes are assayed by comparing the presently available 3D structures. A wide sample of flavoenzymes is analyzed with respect to conserved structural modules and three major structural groups are identified which serve as basic frames for the evolutionary construction of a plethora of flavin-containing redox enzymes. We argue that flavin-based and other types of electron bifurcation are of primordial importance to free energy conversion, the quintessential foundation of life, and discuss a plausible evolutionary ancestry of the mechanism.
电子分叉在此被描述为具有氧化还原协同性的双电子氧化还原化合物可进行的电子转移反应连续体的一种特殊情况。我们认为，电子分叉首先是一种电化学现象，其依据是：(a) 各个氧化还原转变的氧化还原电位强烈反转；(b) 第一个氧化还原转变具有较高的吸能性；(c) 一种逃逸型机制，使得第一个电子转移的完成取决于第二个电子转移的发生。该机制被认为同时支配着传统的基于醌的电子分叉和新发现的基于黄素的电子分叉。通过比较目前可用的三维结构，分析了黄素酶中电子转移伙伴空间排列的保守和可变方面。针对保守的结构模块分析了大量的黄素酶样本，并确定了三个主要结构组，它们作为众多含黄素氧化还原酶进化构建的基本框架。我们认为基于黄素的电子分叉和其他类型的电子分叉对于自由能转换（生命的精髓基础）至关重要，并讨论了该机制可能的进化起源。
