title: Artifactual uncoupling by uncoupling protein 3 in yeast mitochondria at the concentrations found in mouse and rat skeletal-muscle mitochondria.
abstract: Western blots detected uncoupling protein 3 (UCP3) in skeletal-muscle mitochondria from wild-type but not UCP3 knock-out mice. Calibration with purified recombinant UCP3 showed that mouse and rat skeletal muscle contained 0.14 microg of UCP3/mg of mitochondrial protein. This very low UCP3 content is 200-700-fold less than the concentration of UCP1 in brown-adipose-tissue mitochondria from warm-adapted hamster (24-84 microg of UCP1/mg of mitochondrial protein). UCP3 was present in brown-adipose-tissue mitochondria from warm-adapted rats but was undetectable in rat heart mitochondria. We expressed human UCP3 in yeast mitochondria at levels similar to, double and 7-fold those found in rodent skeletal-muscle mitochondria. Yeast mitochondria containing UCP3 were more uncoupled than empty-vector controls, particularly at concentrations that were 7-fold physiological. However, uncoupling by UCP3 was not stimulated by the known activators palmitate and superoxide; neither were they inhibited by GDP, suggesting that the observed uncoupling was a property of non-native protein. As a control, UCP1 was expressed in yeast mitochondria at similar concentrations to that of UCP3 and at up to 50% of the physiological level of UCP1. Low levels of UCP1 gave palmitate-dependent and GDP-sensitive proton conductance but higher levels of UCP1 caused an additional GDP-insensitive uncoupling artifact. We conclude that the uncoupling of yeast mitochondria by high levels of UCP3 expression is entirely an artifact and provides no evidence for any native uncoupling activity of the protein.
authors.affiliation: MRC Dunn Human Nutrition Unit, Hills Road, Cambridge CB2 2XY, U.K.
authors.forename: James A
authors.initials: JA
authors.lastname: Harper
authors.forename: Jeff A
authors.initials: JA
authors.lastname: Stuart
authors.forename: Mika B
authors.initials: MB
authors.lastname: Jekabsons
authors.forename: Damien
authors.initials: D
authors.lastname: Roussel
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Brindle
authors.forename: Keith
authors.initials: K
authors.lastname: Dickinson
authors.forename: Robert B
authors.initials: RB
authors.lastname: Jones
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D002001:Adipose Tissue, Brown / Q000378:metabolism; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D018076:DNA, Complementary / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D002479:Inclusion Bodies / Q000378:metabolism; D007473:Ion Channels; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D008931:Mitochondria, Muscle / Q000378:metabolism*; D024101:Mitochondrial Proteins; D018482:Muscle, Skeletal / Q000378:metabolism; D011522:Protons; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D013481:Superoxides / Q000494:pharmacology; D000071256:Uncoupling Protein 1; D000071247:Uncoupling Protein 3
chemical_list: D002352:Carrier Proteins; D018076:DNA, Complementary; D007473:Ion Channels; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D011522:Protons; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; C000604371:UCP1 protein, human; C000604392:UCP3 protein, human; C000604372:Ucp1 protein, mouse; C000604373:Ucp1 protein, rat; C000604393:Ucp3 protein, mouse; C000604394:Ucp3 protein, rat; D000071256:Uncoupling Protein 1; D000071247:Uncoupling Protein 3; D013481:Superoxides