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Functional flexibility of electron flow between quinol oxidation Q o site of cytochrome bc 1 and cytochrome c revealed by combinatory effects of mutations in cytochrome b, iron-sulfur protein and cytochrome c 1 .

Authors :
Borek A
Ekiert R
Osyczka A
Source :
Biochimica et biophysica acta. Bioenergetics [Biochim Biophys Acta Bioenerg] 2018 Sep; Vol. 1859 (9), pp. 754-761. Date of Electronic Publication: 2018 Apr 27.
Publication Year :
2018

Abstract

Transfer of electron from quinol to cytochrome c is an integral part of catalytic cycle of cytochrome bc <subscript>1</subscript> . It is a multi-step reaction involving: i) electron transfer from quinol bound at the catalytic Q <subscript>o</subscript> site to the Rieske iron-sulfur ([2Fe-2S]) cluster, ii) large-scale movement of a domain containing [2Fe-2S] cluster (ISP-HD) towards cytochrome c <subscript>1</subscript> , iii) reduction of cytochrome c <subscript>1</subscript> by reduced [2Fe-2S] cluster, iv) reduction of cytochrome c by cytochrome c <subscript>1</subscript> . In this work, to examine this multi-step reaction we introduced various types of barriers for electron transfer within the chain of [2Fe-2S] cluster, cytochrome c <subscript>1</subscript> and cytochrome c. The barriers included: impediment in the motion of ISP-HD, uphill electron transfer from [2Fe-2S] cluster to heme c <subscript>1</subscript> of cytochrome c <subscript>1</subscript> , and impediment in the catalytic quinol oxidation. The barriers were introduced separately or in various combinations and their effects on enzymatic activity of cytochrome bc <subscript>1</subscript> were compared. This analysis revealed significant degree of functional flexibility allowing the cofactor chains to accommodate certain structural and/or redox potential changes without losing overall electron and proton transfers capabilities. In some cases inhibitory effects compensated one another to improve/restore the function. The results support an equilibrium model in which a random oscillation of ISP-HD between the Q <subscript>o</subscript> site and cytochrome c <subscript>1</subscript> helps maintaining redox equilibrium between all cofactors of the chain. We propose a new concept in which independence of the dynamics of the Q <subscript>o</subscript> site substrate and the motion of ISP-HD is one of the elements supporting this equilibrium and also is a potential factor limiting the overall catalytic rate.<br /> (Copyright © 2018 Elsevier B.V. All rights reserved.)

Details

Language :
English
ISSN :
0005-2728
Volume :
1859
Issue :
9
Database :
MEDLINE
Journal :
Biochimica et biophysica acta. Bioenergetics
Publication Type :
Academic Journal
Accession number :
29705394
Full Text :
https://doi.org/10.1016/j.bbabio.2018.04.010