Domain movement of iron sulfur protein in cytochrome bc1 complex is facilitated by the electron transfer from cytochrome bL to bH

Cen, Xiaowei; Yu, Linda

doi:10.1016/j.febslet.2008.01.016

Cited by 9 publications

(10 citation statements)

References 33 publications

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“…Recent results (32,33) of analyses of the binding affinity and inhibitory efficacies of P m and P f inhibitors, at different redox states of the cytochrome bc 1 complex, are consistent with this proposal. One way to further substantiate this proposal is to determine the electron transfer activity and pre-steady state reduction rates of hemes c 1 , b L , and b H , by quinol, in the presence and absence of inhibitors, in mutant complexes lacking heme b L or heme b H and compared with those obtained from the wild-type complex.…”

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confidence: 65%

On the Mechanism of Quinol Oxidation at the QP Site in the Cytochrome bc1 Complex

Yang

2008

Journal of Biological Chemistry

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To elucidate the mechanism of bifurcated oxidation of quinol in the cytochrome bc 1 complex, Rhodobacter sphaeroides mutants, H198N and H111N, lacking heme b L and heme b H , respectively, were constructed and characterized. Purified mutant complexes have the same subunit composition as that of the wild-type complex, but have only 9 -11% of the electron transfer activity, which is sensitive to stigmatellin or myxothiazol. The E m values for hemes b L and b H in the H111N and H198N complexes are ؊95 and ؊35 mV, respectively. The pseudo firstorder reduction rate constants for hemes b L and b H in H111N and H198N, by ubiquiniol, are 16.3 and 12.4 s ؊1 , respectively. These indicate that the Q p site in the H111N mutant complex is similar to that in the wild-type complex. Pre-steady state reduction rates of heme c 1 by these two mutant complexes decrease to a similar extent of their activity, suggesting that the decrease in electron transfer activity is due to impairment of movement of the head domain of reduced iron-sulfur protein, caused by disruption of electron transfer from heme b L to heme b H . Both mutant complexes produce as much superoxide as does antimycin A-treated wild-type complex. Ascorbate eliminates all superoxide generating activity in the intact or antimycin inhibited wild-type or mutant complexes.The cytochrome bc 1 complex, also known as complex III or ubiquinol-cytochrome c oxidoreductase, is an essential segment of the electron transfer chain in mitochondria and photosynthetic bacteria (1). The complex catalyzes electron transfer from quinol to cytochrome c (c 2 in some bacteria) with concomitant translocation of protons across the inner membrane of mitochondria or cytoplasmic membrane of bacteria. Intensive biochemical and biophysical studies on this complex (2-4) have led to the formulation of the "protonmotive Q-cycle" mechanism for electron and proton transfer in this complex (5-7). The key step of the Q-cycle mechanism is the bifurcated oxidation of quinol at the quinol oxidation site (Q P ). In the Q-cycle mechanism, it was postulated that the first electron of quinol is transferred to the "high potential chain," consisting of iron-sulfur protein (ISP) 2 and cytochrome c 1 . Then the second electron of quinol, via a transient semiquinone, is passed through the "low potential chain" consisting of cytochromes b L and b H , to reduce ubiquinone or ubisemiquinone bound at the quinol reduction site (Q N ). One drawback of this sequential scheme is the lack of a "functional" semiquinone at the Q P site (8 -10), even though some radicals have been reported under abnormal conditions (11,12). Recently, pre-steady state kinetic analysis of the reduction of cytochrome b L and ISP in a same sample using fast quenching coupled with EPR (13) indicates that both iron-sulfur cluster (ISC) and heme b L are reduced by quinol at the same rate, suggesting a concerted scheme for the bifurcated oxidation of quinol at the Q P site (13,14).Although the concerted mechanism explains why the proposed semiquinone a...

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confidence: 65%

On the Mechanism of Quinol Oxidation at the QP Site in the Cytochrome bc1 Complex

Yang

2008

Journal of Biological Chemistry

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“…There are several mechanistic aspects of the movement of ISP-HD that remain the subject of discussion . One of the most important and still unsolved issues concerns a fundamental question of whether the motion is simply a stochastic, thermally activated process or whether it is rather controlled by a particular state or states of the enzyme during the catalytic cycle. ,− The simplest answer one may consider is that the motion represents a stochastic process of constrained diffusion, ,− which is fast enough (∼80 000 s –1 ) not to limit the overall rate of catalysis . The stochastic diffusion, in contrast to any mechanism that would rely on a specific element or elements of control imposed on the ISP-HD movement, has the clear advantage of not requiring energy expenditure for “information gain” needed to control the cycle.…”

Section: Overview Of Structure and Function Of Cytochromes Bcmentioning

confidence: 99%

“…The role of the ef loop was proposed following the finding that mutations in this region can compensate the effect of +1Ala. , Further mutational studies revealed that bulky side chains located in the middle part of the loop limit the ability of ISP-HD to move outside the Q o site . This led to the proposal that the ef loop acts as a switch increasing or decreasing the rate of electron transfer between the Q o site and heme c 1 , , which together with the cd1 helix constitutes the mechanism of binding and release of ISP-HD depending on the redox state of hemes b . ,,, However, as demonstrated by mutational studies, amino acid side chains such as Rh L286, Rh I292 on the ef loop in fact may serve to resist in transitions between b - and c -position . The control mechanisms steering this loop during the catalytic cycle are a matter of discussion.…”

Section: Overview Of Structure and Function Of Cytochromes Bcmentioning

confidence: 99%

Catalytic Reactions and Energy Conservation in the Cytochrome bc₁ and b₆f Complexes of Energy-Transducing Membranes

et al. 2021

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This review focuses on key components of respiratory and photosynthetic energy-transduction systems: the cytochrome bc 1 and b 6 f (Cytbc 1 /b 6 f) membranous multisubunit homodimeric complexes. These remarkable molecular machines catalyze electron transfer from membranous quinones to water-soluble electron carriers (such as cytochromes c or plastocyanin), coupling electron flow to proton translocation across the energy-transducing membrane and contributing to the generation of a transmembrane electrochemical potential gradient, which powers cellular metabolism in the majority of living organisms. Cytsbc 1 /b 6 f share many similarities but also have significant differences. While decades of research have provided extensive knowledge on these enzymes, several important aspects of their molecular mechanisms remain to be elucidated. We summarize a broad range of structural, mechanistic, and physiological aspects required for function of Cytbc 1 /b 6 f, combining textbook fundamentals with new intriguing concepts that have emerged from more recent studies. The discussion covers but is not limited to (i) mechanisms of energy-conserving bifurcation of electron pathway and energy-wasting superoxide generation at the quinol oxidation site, (ii) the mechanism by which semiquinone is stabilized at the quinone reduction site, (iii) interactions with substrates and specific inhibitors, (iv) intermonomer electron transfer and the role of a dimeric complex, and (v) higher levels of organization and regulation that involve Cytsbc 1 /b 6 f. In addressing these topics, we point out existing uncertainties and controversies, which, as suggested, will drive further research in this field.

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“…One possibility is that the ET from hemes b L to b H causes protein conformational changes in the cd1 helix and allows or forces the reduced ISP-ED to move from the b -position to the c 1 -position to be oxidized [85, 86]. Such a redox-induced conformational change in the cyt b subunit has yet to gain direct experimental support.…”

Section: Mechanism Of Et-coupled Proton Pumping From a Structural mentioning

confidence: 99%

Structural analysis of cytochrome bc1 complexes: Implications to the mechanism of function

Xia¹,

Esser²,

Tang³

et al. 2013

Biochimica et Biophysica Acta (BBA) - Bioenergetics

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174

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Summary The cytochrome bc1 complex (bc1) is the mid-segment of the cellular respiratory chain of mitochondria and many aerobic prokaryotic organisms; it is also part of the photosynthetic apparatus of non-oxygenic purple bacteria. The bc1 complex catalyzes the reaction of transferring electrons from the low potential substrate ubiquinol to high potential cytochrome c. Concomitantly, bc1 translocates protons across the membrane, contributing to the proton-motive force essential for a variety of cellular activities such as ATP synthesis. Structural investigations of bc1 have been exceedingly successful, yielding atomic resolution structures of bc1 from various organisms and trapped in different reaction intermediates. These structures have confirmed and unified results of decades of experiments and have contributed to our understanding of the mechanism of bc1 functions as well as its inactivation by respiratory inhibitors.

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Domain movement of iron sulfur protein in cytochrome bc₁ complex is facilitated by the electron transfer from cytochrome b_L to b_H

Cited by 9 publications

References 33 publications

On the Mechanism of Quinol Oxidation at the QP Site in the Cytochrome bc1 Complex

On the Mechanism of Quinol Oxidation at the QP Site in the Cytochrome bc1 Complex

Catalytic Reactions and Energy Conservation in the Cytochrome bc₁ and b₆f Complexes of Energy-Transducing Membranes

Structural analysis of cytochrome bc1 complexes: Implications to the mechanism of function

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Domain movement of iron sulfur protein in cytochrome bc1 complex is facilitated by the electron transfer from cytochrome bL to bH

Cited by 9 publications

References 33 publications

On the Mechanism of Quinol Oxidation at the QP Site in the Cytochrome bc1 Complex

On the Mechanism of Quinol Oxidation at the QP Site in the Cytochrome bc1 Complex

Catalytic Reactions and Energy Conservation in the Cytochrome bc1 and b6f Complexes of Energy-Transducing Membranes

Structural analysis of cytochrome bc1 complexes: Implications to the mechanism of function

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Domain movement of iron sulfur protein in cytochrome bc₁ complex is facilitated by the electron transfer from cytochrome b_L to b_H

Catalytic Reactions and Energy Conservation in the Cytochrome bc₁ and b₆f Complexes of Energy-Transducing Membranes