Inhibition of electron transfer in the cytochromeb-c 1 segment of the mitochondrial respiratory chain by a synthetic analogue of ubiquinone

Trumpower, Bernard L.; Haggerty, John G.

doi:10.1007/bf00744680

Cited by 71 publications

(32 citation statements)

References 10 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…At pH 7.4, a pH value optimal for enzyme activity 28 , an IC 50 value of 45 nM was obtained, which agrees well with previously published data 25 . As hydroxynaphthoquinones ionize 37 and pH-dependent potency of inhibition has been reported for another ionizable cyt bc 1 inhibitor, 5-n-heptyl-6-hydroxy-4,7-dioxobenzothiazole 38 (HDBT), potency of atovaquone inhibition was monitored for a pH range between 6.5 and 7.4. In this pH range, the uninhibited enzyme activity is within B80% of the maximum turnover 28 .…”

Section: Resultsmentioning

confidence: 99%

Structural analysis of atovaquone-inhibited cytochrome bc1 complex reveals the molecular basis of antimalarial drug action

2014

View full text Add to dashboard Cite

Section: Resultsmentioning

confidence: 99%

Structural analysis of atovaquone-inhibited cytochrome bc1 complex reveals the molecular basis of antimalarial drug action

2014

View full text Add to dashboard Cite

“…Hydroxydioxobenzothiazoles efficiently inhibit the bc 1 complex in a pH-dependent manner (38). It was argued that low efficacy at alkaline pH could be attributed to ionization of the inhibitor due to restricted access to the binding site or to protonation of a functional group within the enzyme (38,44).…”

Section: Discussionmentioning

confidence: 99%

“…The purified bc 1 complex used in this study has a partially reduced Rieske and is fully inhibited by the applied amount of HHDBT (results not shown). A pK a of 6.5 has been determined for the weakly acidic hydroxy group of UHDBT, which was measured in phosphate buffer containing 1% ethanol, and deprotonation of the hydroxy group is manifested by a color change from yellow to rose-violet (38). Here, the complex was crystallized at pH 8.0 as a protein-detergent complex; therefore, the acidity of the hydroxy group was measured in detergent micelles by monitoring the blue shift in the optical spectrum upon ionization.…”

Section: Crystallization Of Hhdbt-inhibited Bcmentioning

confidence: 99%

Structure of the Yeast Cytochrome bc 1 Complex with a Hydroxyquinone Anion Qo Site Inhibitor Bound

Pálsdóttir

Lojero

Trumpower

et al. 2003

Journal of Biological Chemistry

Self Cite

177

215

View full text Add to dashboard Cite

Bifurcated electron transfer during ubiquinol oxidation is the key reaction of cytochrome bc 1 complex catalysis. Binding of the competitive inhibitor 5-n-heptyl-6-hydroxy-4,7-dioxobenzothiazole to the Q o site of the cytochrome bc 1 complex from Saccharomyces cerevisiae was analyzed by x-ray crystallography. This alkylhydroxydioxobenzothiazole is bound in its ionized form as evident from the crystal structure and confirmed by spectroscopic analysis, consistent with a measured pK a ‫؍‬ 6.1 of the hydroxy group in detergent micelles. Stabilizing forces for the hydroxyquinone anion inhibitor include a polarized hydrogen bond to the iron-sulfur cluster ligand His 181 and on-edge interactions via weak hydrogen bonds with cytochrome b residue Tyr 279 . The hydroxy group of the latter contributes to stabilization of the Rieske protein in the b-position by donating a hydrogen bond. The reported pH dependence of inhibition with lower efficacy at alkaline pH is attributed to the protonation state of His 181 with a pK a of 7.5. Glu 272 , a proposed primary ligand and proton acceptor of ubiquinol, is not bound to the carbonyl group of the hydroxydioxobenzothiazole ring but is rotated out of the binding pocket toward the heme b L propionate A, to which it is hydrogen-bonded via a single water molecule. The observed hydrogen bonding pattern provides experimental evidence for the previously proposed proton exit pathway involving the heme propionate and a chain of water molecules. Binding of the alkyl-6-hydroxy-4,7-dioxobenzothiazole is discussed as resembling an intermediate step of ubiquinol oxidation, supporting a single occupancy model at the Q o site.Ubiquinol:cytochrome c oxidoreductase (cytochrome bc 1 complex, EC 1.10.2.2 (bc 1 complex)) is a multisubunit membrane protein complex, which is one of the fundamental components of respiratory and photosynthetic electron transfer chains. The enzyme catalyzes electron transfer from ubiquinol to cytochrome c and couples this process to electrogenic translocation of protons across the membrane (1, 2). Each functional unit of the homodimeric complex consists of three catalytic subunits: cytochrome b with two b type hemes, cytochrome c 1 with one c type heme, and the Rieske protein containing a [2Fe-2S] cluster. Mitochondrial bc 1 complexes contain up to eight additional subunits. Structures of vertebrate and yeast bc 1 complexes were determined, providing a breakthrough in understanding the enzyme mechanism and structure-function relationships within the enzyme (3-7). The 2.3-Å resolution structure from the yeast Saccharomyces cerevisiae has the highest resolution available so far. It allowed a detailed description of substrate and inhibitor binding sites, elucidating parts of the enzyme mechanism and suggesting pathways for proton transfer.The mechanism of the enzyme known as the protonmotive Q cycle (8) involves separate catalytic sites for ubiquinol oxidation (Q o site) and ubiquinone reduction (Q i site). Protons are taken up from the matrix side when ubiquinone is reduced a...

show abstract

“…2,3-Dimethoxyl-5-methyl-6-geranyl-4-benzoquinone (Q 2 ), its reduced form (Q 2 H 2 ) (19), and UHDBT (20,21) were synthesized as previously reported. Other chemicals were of the highest purity commercially available.…”

Section: Methodsmentioning

confidence: 99%

pH-induced Intramolecular Electron Transfer between the Iron-Sulfur Protein and Cytochrome c 1 in Bovine Cytochrome bc 1 Complex

Zhang

Tai

2000

Journal of Biological Chemistry

View full text Add to dashboard Cite

Structural analysis of the bc 1 complex suggests that the extramembrane domain of iron-sulfur protein (ISP) undergoes substantial movement during the catalytic cycle. Binding of Qo site inhibitors to this complex affects the mobility of ISP. Taking advantage of the difference in the pH dependence of the redox midpoint potentials of cytochrome c 1 and ISP, we have measured electron transfer between the [2Fe-2S] cluster and heme c 1 in native and inhibitor-treated partially reduced cytochrome bc 1 complexes. The rate of the pH-induced cytochrome c 1 reduction can be estimated by conventional stopped-flow techniques (t1 ⁄2 , 1-2 ms), whereas the rate of cytochrome c 1 oxidation is too high for stoppedflow measurement. These results suggest that oxidized ISP has a higher mobility than reduced ISP and that the movement of reduced ISP may require an energy input from another component. In the 5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole (UHDBT)-inhibited complex, the rate of cytochrome c 1 reduction is greatly decreased to a t1 ⁄2 of approximately 2.8 s. An even lower rate is observed with the stigmatellin-treated complex. These results support the idea that UHDBT and stigmatellin arrest the [2Fe-2S] cluster at a fixed position, 31 Å from heme c 1 , making electron transfer very slow.The cytochrome bc 1 complex is a segment of the mitochondrial respiratory chain which catalyzes antimycin-sensitive electron transfer from ubiquinol to cytochrome c (1, 2). The reaction is coupled to the translocation of protons across the mitochondrial inner membrane to generate a proton gradient and membrane potential for ATP synthesis (2-4). The purified cytochrome bc 1 complex contains 11 protein subunits, 2165 amino acid residues, and 4 prosthetic groups with a total molecular mass of 248 kDa, without counting the bound phospholipids. The amino acid sequences of all subunits are available from either peptide or nucleotide sequencing (5, 6). The essential redox components of the complex are: two b-type cytochromes (heme b L , E m 1 ϭ Ϫ30 mV, heme b H, , E m ϭ 90 mV), one c-type cytochrome (heme c 1 , E m ϭ 227 mV), one high potential [2Fe-2S] cluster (FeS, E m ϭ 280 mV), and a ubiquinone. The three-dimensional structure of cytochrome bc 1 complex at 2.9 Å resolution was first reported in 1997 (5, 7). More complete structures, from a different crystalline form, have been reported recently (8 -10). The crystal structure of the complex exists as a closely interacting functional dimer. There are 13 transmembrane helices in each monomer, 8 belong to cytochrome b, and one each to cytochrome c 1 , ISP, and subunits 7, 10, and 11. The 21 Å between heme b L and heme b H and 27 Å between heme b L and the [2Fe-2S] cluster accommodate well the observed fast electron transfer between these redox centers (11, 12). However, the 31 Å between the [2Fe-2S] cluster and heme c 1 makes it difficult to explain the high electron transfer rates between them.During analysis of x-ray diffraction data of the crystalline complex (7), it was noticed that the extr...

show abstract

Inhibition of electron transfer in the cytochromeb-c 1 segment of the mitochondrial respiratory chain by a synthetic analogue of ubiquinone

Cited by 71 publications

References 10 publications

Structural analysis of atovaquone-inhibited cytochrome bc1 complex reveals the molecular basis of antimalarial drug action

Structural analysis of atovaquone-inhibited cytochrome bc1 complex reveals the molecular basis of antimalarial drug action

Structure of the Yeast Cytochrome bc 1 Complex with a Hydroxyquinone Anion Qo Site Inhibitor Bound

pH-induced Intramolecular Electron Transfer between the Iron-Sulfur Protein and Cytochrome c 1 in Bovine Cytochrome bc 1 Complex

Contact Info

Product

Resources

About