The High-Spin Heme bL Mutant Exposes Dominant Reaction Leading to the Formation of the Semiquinone Spin-Coupled to the [2Fe-2S]+ Cluster at the Qo Site of Rhodobacter capsulatus Cytochrome bc1
Open Access
- 7 May 2021
- journal article
- research article
- Published by Frontiers Media SA in Frontiers in Chemistry
Abstract
Cytochrome bc1 (mitochondrial complex III) catalyzes electron transfer from quinols to cytochrome c and couples this reaction with proton translocation across lipid membrane; thus, it contributes to the generation of protonmotive force used for the synthesis of ATP. The energetic efficiency of the enzyme relies on a bifurcation reaction taking place at the Qo site which upon oxidation of ubiquinol directs one electron to the Rieske 2Fe2S cluster and the other to heme bL. The molecular mechanism of this reaction remains unclear. A semiquinone spin-coupled to the reduced 2Fe2S cluster (SQo-2Fe2S) was identified as a state associated with the operation of the Qo site. To get insights into the mechanism of the formation of this state, we first constructed a mutant in which one of the histidine ligands of the iron ion of heme bLRhodobacter capsulatus cytochrome bc1 was replaced by asparagine (H198N). This converted the low-spin, low-potential heme into the high-spin, high-potential species which is unable to support enzymatic turnover. We performed a comparative analysis of redox titrations of antimycin-supplemented bacterial photosynthetic membranes containing native enzyme and the mutant. The titrations revealed that H198N failed to generate detectable amounts of SQo-2Fe2S under neither equilibrium (in dark) nor nonequilibrium (in light), whereas the native enzyme generated clearly detectable SQo-2Fe2S in light. This provided further support for the mechanism in which the back electron transfer from heme bL to a ubiquinone bound at the Qo site is mainly responsible for the formation of semiquinone trapped in the SQo-2Fe2S state in R. capusulatus cytochrome bc1.Keywords
Funding Information
- Narodowe Centrum Nauki
This publication has 67 references indexed in Scilit:
- Enzymatic Activities of Isolated Cytochrome bc1-like Complexes Containing Fused Cytochrome b Subunits with Asymmetrically Inactivated Segments of Electron Transfer ChainsBiochemistry, 2012
- Fusing two cytochromes b of Rhodobacter capsulatus cytochrome bc1 using various linkers defines a set of protein templates for asymmetric mutagenesis"Protein Engineering, Design and Selection", 2011
- Discrimination between two possible reaction sequences that create potential risk of generation of deleterious radicals by cytochrome bc1: Implications for the mechanism of superoxide productionBiochimica et Biophysica Acta (BBA) - Bioenergetics, 2010
- Visualizing changes in electron distribution in coupled chains of cytochrome bc1 by modifying barrier for electron transfer between the FeS cluster and heme c1Biochimica et Biophysica Acta (BBA) - Bioenergetics, 2010
- Magnetic Interactions Sense Changes in Distance between Heme bL and the Iron−Sulfur Cluster in Cytochrome bc1Biochemistry, 2009
- Quinone and non-quinone redox couples in Complex IIIJournal of Bioenergetics and Biomembranes, 2008
- On the Mechanism of Quinol Oxidation at the QP Site in the Cytochrome bc1 Complex: STUDIED USING MUTANTS LACKING CYTOCHROME bL OR bHOnline Journal of Public Health Informatics, 2008
- Exposing the Complex III Qo semiquinone radicalBiochimica et Biophysica Acta (BBA) - Bioenergetics, 2007
- A semiquinone intermediate generated at the Q o site of the cytochrome bc 1 complex: Importance for the Q-cycle and superoxide productionProceedings of the National Academy of Sciences of the United States of America, 2007
- Simultaneous reduction of iron–sulfur protein and cytochrome b L during ubiquinol oxidation in cytochrome bc 1 complexProceedings of the National Academy of Sciences of the United States of America, 2007