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Direct and mediated electron transfer between intact succinate:quinone oxidoreductase from Bacillus subtilis and a surface modified gold electrode reveals redox state-dependent conformational changes.

Christenson, Andreas LU ; Gustavsson, Tobias LU ; Gorton, Lo LU and Hägerhäll, Cecilia LU (2008) In Biochimica et Biophysica Acta - Bioenergetics 1777(9). p.1203-1210
Abstract
Succinate:quinone oxidoreductase (SQR) from Bacillus subtilis consists of two hydrophilic protein subunits comprising succinate dehydrogenase, and a di-heme membrane anchor protein harboring two putative quinone binding sites, Q(p) and Q(d). In this work we have used spectroelectrochemistry to study the electronic communication between purified SQR and a surface modified gold capillary electrode. In the presence of two soluble quinone mediators the midpoint potentials of both hemes were revealed essentially as previously determined by conventional redox titration (heme b(H), E(m)=+65 mV, heme b(L), E(m)=-95 mV). In the absence of mediators the enzyme still communicated with the electrode, albeit with a reproducible hysteresis, resulting in... (More)
Succinate:quinone oxidoreductase (SQR) from Bacillus subtilis consists of two hydrophilic protein subunits comprising succinate dehydrogenase, and a di-heme membrane anchor protein harboring two putative quinone binding sites, Q(p) and Q(d). In this work we have used spectroelectrochemistry to study the electronic communication between purified SQR and a surface modified gold capillary electrode. In the presence of two soluble quinone mediators the midpoint potentials of both hemes were revealed essentially as previously determined by conventional redox titration (heme b(H), E(m)=+65 mV, heme b(L), E(m)=-95 mV). In the absence of mediators the enzyme still communicated with the electrode, albeit with a reproducible hysteresis, resulting in the reduction of both hemes occurring approximately at the midpoint potential of heme b(L), and with a pronounced delay of reoxidation. When the specific inhibitor 2-n-heptyl-4 hydroxyquinoline N-oxide (HQNO), which binds to Q(d) in B. subtilis SQR, was added together with the two quinone mediators, rapid reductive titration was still possible which can be envisioned as an electron transfer occurring via the HQNO insensitive Q(p) site. In contrast, the subsequent oxidative titration was severely hampered in the presence of HQNO, in fact it completely resembled the unmediated reaction. If mediators communicate with Q(p) or Q(d), either event is followed by very rapid electron redistribution within the enzyme. Taken together, this strongly suggests that the accessibility of Q(p) depended on the redox state of the hemes. When both hemes were reduced, and Q(d) was blocked by HQNO, quinone-mediated communication via the Q(p) site was no longer possible, revealing a redox-dependent conformational change in the membrane anchor domain. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Mercaptohexanol, Spectroelectrochemistry, Quinone, QFR, SdhC, Cytochrome b, SQR, Gold capillary
in
Biochimica et Biophysica Acta - Bioenergetics
volume
1777
issue
9
pages
1203 - 1210
publisher
Elsevier
external identifiers
  • wos:000259287200015
  • pmid:18598669
  • scopus:50949128131
ISSN
0005-2728
DOI
10.1016/j.bbabio.2008.05.450
language
English
LU publication?
yes
id
1e94252c-e444-4fcb-8d1b-4dd52ff0bb7c (old id 1181585)
date added to LUP
2008-10-20 09:43:57
date last changed
2017-06-18 03:59:32
@article{1e94252c-e444-4fcb-8d1b-4dd52ff0bb7c,
  abstract     = {Succinate:quinone oxidoreductase (SQR) from Bacillus subtilis consists of two hydrophilic protein subunits comprising succinate dehydrogenase, and a di-heme membrane anchor protein harboring two putative quinone binding sites, Q(p) and Q(d). In this work we have used spectroelectrochemistry to study the electronic communication between purified SQR and a surface modified gold capillary electrode. In the presence of two soluble quinone mediators the midpoint potentials of both hemes were revealed essentially as previously determined by conventional redox titration (heme b(H), E(m)=+65 mV, heme b(L), E(m)=-95 mV). In the absence of mediators the enzyme still communicated with the electrode, albeit with a reproducible hysteresis, resulting in the reduction of both hemes occurring approximately at the midpoint potential of heme b(L), and with a pronounced delay of reoxidation. When the specific inhibitor 2-n-heptyl-4 hydroxyquinoline N-oxide (HQNO), which binds to Q(d) in B. subtilis SQR, was added together with the two quinone mediators, rapid reductive titration was still possible which can be envisioned as an electron transfer occurring via the HQNO insensitive Q(p) site. In contrast, the subsequent oxidative titration was severely hampered in the presence of HQNO, in fact it completely resembled the unmediated reaction. If mediators communicate with Q(p) or Q(d), either event is followed by very rapid electron redistribution within the enzyme. Taken together, this strongly suggests that the accessibility of Q(p) depended on the redox state of the hemes. When both hemes were reduced, and Q(d) was blocked by HQNO, quinone-mediated communication via the Q(p) site was no longer possible, revealing a redox-dependent conformational change in the membrane anchor domain.},
  author       = {Christenson, Andreas and Gustavsson, Tobias and Gorton, Lo and Hägerhäll, Cecilia},
  issn         = {0005-2728},
  keyword      = {Mercaptohexanol,Spectroelectrochemistry,Quinone,QFR,SdhC,Cytochrome b,SQR,Gold capillary},
  language     = {eng},
  number       = {9},
  pages        = {1203--1210},
  publisher    = {Elsevier},
  series       = {Biochimica et Biophysica Acta - Bioenergetics},
  title        = {Direct and mediated electron transfer between intact succinate:quinone oxidoreductase from Bacillus subtilis and a surface modified gold electrode reveals redox state-dependent conformational changes.},
  url          = {http://dx.doi.org/10.1016/j.bbabio.2008.05.450},
  volume       = {1777},
  year         = {2008},
}