Mutations in Mitochondrial Complex III Uniquely Affect Complex I in Caenorhabditis elegans

Abstract

Mitochondrial supercomplexes containing complexes I, III, and IV of the electron transport chain are now regarded as an established entity. Supercomplex I·III·IV has been theorized to improve respiratory chain function by allowing quinone channeling between complexes I and III. Here, we show that the role of the supercomplexes extends beyond channeling. Mutant analysis in Caenorhabditis elegans reveals that complex III affects supercomplex I·III·IV formation by acting as an assembly or stabilizing factor. Also, a complex III mtDNA mutation, ctb-1, inhibits complex I function by weakening the interaction of complex IV in supercomplex I·III·IV. Other complex III mutations inhibit complex I function either by decreasing the amount of complex I (isp-1), or decreasing the amount of complex I in its most active form, the I·III·IV supercomplex (isp-1;ctb-1). ctb-1 suppresses a nuclear encoded complex III defect, isp-1, without improving complex III function. Allosteric interactions involve all three complexes within the supercomplex and are necessary for maximal enzymatic activities. Mitochondrial supercomplexes containing complexes I, III, and IV of the electron transport chain are now regarded as an established entity. Supercomplex I·III·IV has been theorized to improve respiratory chain function by allowing quinone channeling between complexes I and III. Here, we show that the role of the supercomplexes extends beyond channeling. Mutant analysis in Caenorhabditis elegans reveals that complex III affects supercomplex I·III·IV formation by acting as an assembly or stabilizing factor. Also, a complex III mtDNA mutation, ctb-1, inhibits complex I function by weakening the interaction of complex IV in supercomplex I·III·IV. Other complex III mutations inhibit complex I function either by decreasing the amount of complex I (isp-1), or decreasing the amount of complex I in its most active form, the I·III·IV supercomplex (isp-1;ctb-1). ctb-1 suppresses a nuclear encoded complex III defect, isp-1, without improving complex III function. Allosteric interactions involve all three complexes within the supercomplex and are necessary for maximal enzymatic activities. IntroductionA solid-state model (1Chance B. Williams G.R. Nature. 1955; 176: 250-254Crossref PubMed Scopus (197) Google Scholar) of the mitochondrial respiratory chain within the mitochondrial membrane was proposed a half-century ago. In this model, the respiratory complexes are assembled into multicomplex structures, supercomplexes. Supercomplexes are capable of substrate channeling and thus facilitate transfer of electrons from one complex to the next (2Bianchi C. Genova M.L. Parenti Castelli G. Lenaz G. J. Biol. Chem. 2004; 279: 36562-36569Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar). This is in contrast to the random collision model (3Hackenbrock C.R. Chazotte B. Gupte S.S. J. Bioenerg. Biomembr. 1986; 18: 331-368Crossref PubMed Scopus (278) Google Scholar), which proposes that the complexes of the mitochondrial respiratory chain are embedded in the inner mitochondrial membrane as separate entities. Individual complexes are functionally connected to each other by the small, mobile electron carriers, coenzyme Q, and cytochrome c. The random collision model became more generally accepted as kinetic studies demonstrated homogenous pool behavior of coenzyme Q (4Kröger A. Klingenberg M. Eur. J. Biochem. 1973; 39: 313-323Crossref PubMed Scopus (170) Google Scholar), rates of electron transfer that did not require substrate channeling, and the successful isolation of individual respiratory complexes that were enzymatically active (3Hackenbrock C.R. Chazotte B. Gupte S.S. J. Bioenerg. Biomembr. 1986; 18: 331-368Crossref PubMed Scopus (278) Google Scholar, 5Hatefi Y. Haavik A.G. Griffiths D.E. J. Biol. Chem. 1962; 237: 1676-1680Abstract Full Text PDF PubMed Google Scholar). However, supercomplex structures containing complexes I, III, and IV, have been investigated by blue native polyacrylamide gel electrophoresis (BN-PAGE), 3The abbreviations used are: BN-PAGEblue native polyacrylamide gel electrophoresisETCelectron transport chainIGAin-gel activityBNGblue native gelhrCNEhigh resolution clear native electrophoresismAbmonoclonal antibodyISPiron sulfur proteinL3larval stage 3L4larval stage 4. sucrose gradient centrifugation, and single particle analysis (6Dudkina N.V. Eubel H. Keegstra W. Boekema E.J. Braun H.P. Proc. Natl. Acad. Sci. U.S.A. 2005; 102: 3225-3229Crossref PubMed Scopus (263) Google Scholar, 7Schäfer E. Dencher N.A. Vonck J. Parcej D.N. Biochemistry. 2007; 46: 12579-12585Crossref PubMed Scopus (134) Google Scholar). A recent study by Acin-Perez et al. (8Acín-Pérez R. Fernández-Silva P. Peleato M.L. Pérez-Martos A. Enriquez J.A. Mol. Cell. 2008; 32: 529-539Abstract Full Text Full Text PDF PubMed Scopus (568) Google Scholar) convincingly showed that supercomplexes are functional units capable of consuming oxygen when provided appropriate electron donors. They concluded that supercomplexes are in fact the functional respiratory unit of the mitochondrion in vivo. Schagger and Pfeiffer (9Schägger H. Pfeiffer K. EMBO J. 2000; 19: 1777-1783Crossref PubMed Scopus (1013) Google Scholar) demonstrated that supercomplex I·III·IV appears on blue native gels (BNGs) with increasing stoichiometries of complex IV. They termed these entities S0–S4, where the numeral denotes the number of complex IVs within the supercomplex.Supercomplexes provide a logical explanation for combined deficiencies of the electron transport chain (ETC) observed in patients. It is estimated that ∼30% of all ETC disorders involve multiple complexes (10Smits P. Mattijssen S. Morava E. van den Brand M. van den Brandt F. Wijburg F. Pruijn G. Smeitink J. Nijtmans L. Rodenburg R. van den Heuvel L. Eur. J. Hum. Genet. 2010; 18: 324-329Crossref PubMed Scopus (28) Google Scholar). Combined I·IV deficiencies (11Benecke R. Strümper P. Weiss H. Brain. 1993; 116: 1451-1463Crossref PubMed Scopus (190) Google Scholar, 12Brass E.P. Hiatt W.R. Gardner A.W. Hoppel C.L. Am. J. Physiol. Heart Circ. Physiol. 2001; 280: H603-H609Crossref PubMed Google Scholar, 13Korenke G.C. Bentlage H.A. Ruitenbeek W. Sengers R.C. Sperl W. Trijbels J.M. Gabreels F.J. Wijburg F.A. Wiedermann V. Hanefeld F. et al.Eur. J. Pediatr. 1990; 150: 104-108Crossref PubMed Scopus (25) Google Scholar, 14van Straaten H.L. van Tintelen J.P. Trijbels J.M. van den Heuvel L.P. Troost D. Rozemuller J.M. Duran M. de Vries L.S. Schuelke M. Barth P.G. Neuropediatrics. 2005; 36: 193-199Crossref PubMed Scopus (29) Google Scholar), as well as multiple examples of combined I·III deficiencies have been reported (15Schägger H. de Coo R. Bauer M.F. Hofmann S. Godinot C. Brandt U. J. Biol. Chem. 2004; 279: 36349-36353Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar, 16Budde S.M. van den Heuvel L.P. Janssen A.J. Smeets R.J. Buskens C.A. DeMeirleir L. Van Coster R. Baethmann M. Voit T. Trijbels J.M. Smeitink J.A. Biochem. Biophys. Res. Commun. 2000; 275: 63-68Crossref PubMed Scopus (162) Google Scholar, 17Lamantea E. Carrara F. Mariotti C. Morandi L. Tiranti V. Zeviani M. Neuromuscul. Disord. 2002; 12: 49-52Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar). In most eukaryotes, complex III is composed of 11 subunits (18Iwata S. Lee J.W. Okada K. Lee J.K. Iwata M. Rasmussen B. Link T.A. Ramaswamy S. Jap B.K. Science. 1998; 281: 64-71Crossref PubMed Scopus (1055) Google Scholar, 19Xia D. Yu C.A. Kim H. Xia J.Z. Kachurin A.M. Zhang L. Yu L. Deisenhofer J. Science. 1997; 277: 60-66Crossref PubMed Scopus (867) Google Scholar), of which only cytochrome b is encoded by the mitochondrial genome. The catalytic core of complex III is comprised of cytochrome b, ISP (iron sulfur protein; Rieske protein), and cytochrome c1. Most of the mutations in cytochrome b cause isolated complex III deficiencies. However, there is a subset of cytochrome b mutations that cause combined I·III deficiencies, both in patients (15Schägger H. de Coo R. Bauer M.F. Hofmann S. Godinot C. Brandt U. J. Biol. Chem. 2004; 279: 36349-36353Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar, 16Budde S.M. van den Heuvel L.P. Janssen A.J. Smeets R.J. Buskens C.A. DeMeirleir L. Van Coster R. Baethmann M. Voit T. Trijbels J.M. Smeitink J.A. Biochem. Biophys. Res. Commun. 2000; 275: 63-68Crossref PubMed Scopus (162) Google Scholar, 17Lamantea E. Carrara F. Mariotti C. Morandi L. Tiranti V. Zeviani M. Neuromuscul. Disord. 2002; 12: 49-52Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar, 20Blakely E.L. Mitchell A.L. Fisher N. Meunier B. Nijtmans L.G. Schaefer A.M. Jackson M.J. Turnbull D.M. Taylor R.W. FEBS J. 2005; PubMed Scopus Google Scholar) and in R. Fernández-Silva P. R. Pérez-Martos A. C. J.A. Mol. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). In of cytochrome has been reported to to of both complexes I and IV in J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). these has been that assembled complex III, functional or is for the assembly and of complex mutations in ISP or cytochrome have been reported in However, complex III deficiencies in patients are by mutations in E. M. P. Carrara F. L. E. A. G. Zeviani M. Hum. Mol. Genet. 2007; PubMed Scopus Google Scholar, P. A. M. A. J.W. E. D. N. A. de P. A. P. A. Genet. 2001; PubMed Scopus Google Scholar, L. S. E. B. A. E. W. Van Coster R. Am. J. Genet. A. PubMed Scopus Google Scholar), a of ISP in the complex III K. H. W. EMBO J. 18: PubMed Scopus Google Scholar, A. EMBO J. PubMed Scopus Google Scholar). are that in complex III the function of assembled complex I without decreasing the amount of complex Caenorhabditis complex III a in the of and J. F. S. Cell. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar) reported that oxygen to oxygen and A in a complex III cytochrome b, was as a of a of an in the of with J. F. S. Cell. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). However, the cause of this is show that a of complex III, by a in the amount of assembled complex I without a in the amount of assembled complex III. we that ctb-1 complex I function without decreasing either the amount of assembled complex I or the of complex I in supercomplexes. In we show that the of with not from complex III function. on complex I from the of a into complex III. In this the of supercomplex that the of supercomplexes is on The of complex I and III in a model that supercomplexes a role in enzymatic of complexes I and III. The of the between of the ETC has for the of patients with in multiple have in the in complex III the function of complex This without decreasing the amount of complex III or the amount or the of complex I in supercomplexes we that in ctb-1 the of J. F. S. Cell. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar) by complex III with isp-1, complex III in was not by the complex I was which was the only in mitochondrial function that we that an interaction between complexes I and III is the of ctb-1 of the of from to and to is by a in mitochondrial J. J. A. A. Res. PubMed Scopus Google Scholar, Biochem. Biophys. Res. Commun. 2002; PubMed Scopus (134) Google Scholar), which has been to Biochem. Biophys. Res. Commun. 2002; PubMed Scopus (134) Google Scholar). and the in as did ctb-1 or that the mitochondrial deficiencies in and are each more in were by in and ctb-1 the and a number of as its of was This was the only observed in ctb-1, which we as a of mitochondrial we is a of a which is in the of ISP (18Iwata S. Lee J.W. Okada K. Lee J.K. Iwata M. Rasmussen B. Link T.A. Ramaswamy S. Jap B.K. Science. 1998; 281: 64-71Crossref PubMed Scopus (1055) Google Scholar). This has been to for the of the for an of the of the Rieske S. M. Link T.A. H. Full Text Full Text PDF PubMed Scopus Google Scholar). an of the ISP by the of the and complex III a that is to the of the in in was to the of the T. A. J. Mol. Biol. PubMed Scopus Google Scholar). was not to a in complex III of the is the of a in the ISP that affects complex III function in of the complex III deficiencies in which are with the are by the mutations of E. M. P. Carrara F. L. E. A. G. Zeviani M. Hum. Mol. Genet. 2007; PubMed Scopus Google Scholar, P. A. M. A. J.W. E. D. N. A. de P. A. P. A. Genet. 2001; PubMed Scopus Google Scholar, L. S. E. B. A. E. W. Van Coster R. Am. J. Genet. A. PubMed Scopus Google Scholar), a in ISP ctb-1 is a to the of of cytochrome b that is to the and of the Rieske electron transfer (18Iwata S. Lee J.W. Okada K. Lee J.K. Iwata M. Rasmussen B. Link T.A. Ramaswamy S. Jap B.K. Science. 1998; 281: 64-71Crossref PubMed Scopus (1055) Google Scholar). The is not a and not the of cytochrome is not that the in complex III in ctb-1 was not as as in In the of the ctb-1 and mutations are not (18Iwata S. Lee J.W. Okada K. Lee J.K. Iwata M. Rasmussen B. Link T.A. Ramaswamy S. Jap B.K. Science. 1998; 281: 64-71Crossref PubMed Scopus (1055) Google Scholar, 19Xia D. Yu C.A. Kim H. Xia J.Z. Kachurin A.M. Zhang L. Yu L. Deisenhofer J. Science. 1997; 277: 60-66Crossref PubMed Scopus (867) Google Scholar) and not to not that the mutations not to complex III function. complex III of assembled complex III complex III the in ctb-1, which complex III the amount of assembled complex I, which to its complex I with I in is to of complex However, we have that complex I is more active in the I·III·IV supercomplex in the I·III form, as in E. H. F. Dencher N.A. Vonck J. J. Biol. Chem. 281: Full Text Full Text PDF PubMed Scopus Google Scholar). in the the amount of supercomplex I·III·IV to supercomplex I·III is for the complex I as is the for complex IV mutations in C. elegans W. P.G. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). It most a of the of ctb-1 on complex IV within the supercomplex the amount of complex I in the is to improve complex I function with has complex I a of supercomplex I·III and I·III·IV and a amount of complex ctb-1 complex I in its most active form, the I·III·IV The explanation that this the of the supercomplex I·III·IV that complex IV is to the complex I enzymatic rates of its I·III the of supercomplex I·III to I·III·IV in a of this of ctb-1 in the and the that the in the was the as in that complex III interactions between of the I·III·IV supercomplex in this we an of the supercomplex to complex III complex IV from supercomplexes more the In was into supercomplexes were to and as we that was supercomplex containing of complex IV. The supercomplex to either and ctb-1, that these mutations that supercomplex we the that complex III mutations supercomplexes that complex IV its on supercomplex I·III·IV and complex I to a of supercomplex complex III and IV the of complex I E. H. F. Dencher N.A. Vonck J. J. Biol. Chem. 281: Full Text Full Text PDF PubMed Scopus Google Scholar) where the of complex I is to U. Biophys. 1997; PubMed Scopus (197) Google Scholar, R. Nature. 2010; PubMed Scopus Google Scholar). Q in the the for R. Nature. 2010; PubMed Scopus Google Scholar, T. J. Bioenerg. Biomembr. 2001; PubMed Scopus Google Scholar, U. Biochem. PubMed Scopus Google Scholar). in the of subunits in the of complex I, which a core of the in complex I S. E. H. A. T. Biochemistry. 2005; PubMed Scopus Google Scholar, E. A. T. Biochemistry. 2005; PubMed Scopus Google Scholar, J. E. A. T. J. Biol. Chem. 2007; Full Text Full Text PDF PubMed Scopus (77) Google Scholar, S. M. E. A. T. J. Biol. Chem. 2004; 279: Full Text Full Text PDF PubMed Scopus Google Scholar). The interaction between complex IV and other of the supercomplexes in the to an and of the which Q in the A complex I in supercomplex I·III is not as active as complex I in supercomplex complex III both complex I and complex complex IV was in all most in and the amount of complex IV in these mitochondrial B. V. T. J. Mol. Biochem. 1997; PubMed Scopus Google Scholar, J. B. Biol. Chem. 1998; PubMed Scopus Google Scholar) by acting as a of S. F. B. Eur. J. Biochem. 1998; PubMed Scopus Google Scholar). A as is in the complex III complex IV However, complex IV in ETC was not in complex III with the mitochondrial are in ETC between are A recent study by and W. S. Cell. 2010; PubMed Scopus Google Scholar) demonstrated enzymatic of complexes and complexes in isp-1, rates of complexes were more complexes This is They did not complex III or complex I and all rates were to It is to between studies and of and W. S. Cell. 2010; PubMed Scopus Google Scholar), the between are not three in the of that in complex I assembly or A model of supercomplex assembly proposes that the of complex I with the assembled complex III and IV, to a which the supercomplex M. M. Biophys. PubMed Scopus Google Scholar). a of the and Q combined with and assembled complex III and IV. This that the in the ISP supercomplex the to of the In with assembled complexes III and and a of the Q and an of the the we well to proposed assembly of complex I, we have not that in of a between complexes I and III is to involve ISP of complex III and the and subunits of the Q of complex mutations in complex I of complex III C. Janssen R.J. van den Heuvel L.P. Smeitink J.A. Nijtmans L.G. Hum. Mol. Genet. 2004; PubMed Scopus Google Scholar). the in an in the mobile of the is to this a complex However, a assembly or of the supercomplex in The of in the this is that ctb-1 complex I function in an without complex III function. The of complex III subunits on complex I an subunits of the catalytic core supercomplex assembly (isp-1), of supercomplexes or complex I electron in the of and of supercomplexes This is the of a complex III that complex I in this study a into the role of supercomplexes in ETC I and III have and interactions a between complexes of the mitochondrial (9Schägger H. Pfeiffer K. EMBO J. 2000; 19: 1777-1783Crossref PubMed Scopus (1013) Google Scholar, H. de Coo R. Bauer M.F. Hofmann S. Godinot C. Brandt U. J. Biol. Chem. 2004; 279: 36349-36353Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar). of patients with mitochondrial which is into the of in the ETC that from a single a in a single of the ETC have and on mitochondrial function. IntroductionA solid-state model (1Chance B. Williams G.R. Nature. 1955; 176: 250-254Crossref PubMed Scopus (197) Google Scholar) of the mitochondrial respiratory chain within the mitochondrial membrane was proposed a half-century ago. In this model, the respiratory complexes are assembled into multicomplex structures, supercomplexes. Supercomplexes are capable of substrate channeling and thus facilitate transfer of electrons from one complex to the next (2Bianchi C. Genova M.L. Parenti Castelli G. Lenaz G. J. Biol. Chem. 2004; 279: 36562-36569Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar). This is in contrast to the random collision model (3Hackenbrock C.R. Chazotte B. Gupte S.S. J. Bioenerg. Biomembr. 1986; 18: 331-368Crossref PubMed Scopus (278) Google Scholar), which proposes that the complexes of the mitochondrial respiratory chain are embedded in the inner mitochondrial membrane as separate entities. Individual complexes are functionally connected to each other by the small, mobile electron carriers, coenzyme Q, and cytochrome c. The random collision model became more generally accepted as kinetic studies demonstrated homogenous pool behavior of coenzyme Q (4Kröger A. Klingenberg M. Eur. J. Biochem. 1973; 39: 313-323Crossref PubMed Scopus (170) Google Scholar), rates of electron transfer that did not require substrate channeling, and the successful isolation of individual respiratory complexes that were enzymatically active (3Hackenbrock C.R. Chazotte B. Gupte S.S. J. Bioenerg. Biomembr. 1986; 18: 331-368Crossref PubMed Scopus (278) Google Scholar, 5Hatefi Y. Haavik A.G. Griffiths D.E. J. Biol. Chem. 1962; 237: 1676-1680Abstract Full Text PDF PubMed Google Scholar). However, supercomplex structures containing complexes I, III, and IV, have been investigated by blue native polyacrylamide gel electrophoresis (BN-PAGE), 3The abbreviations used are: BN-PAGEblue native polyacrylamide gel electrophoresisETCelectron transport chainIGAin-gel activityBNGblue native gelhrCNEhigh resolution clear native electrophoresismAbmonoclonal antibodyISPiron sulfur proteinL3larval stage 3L4larval stage 4. sucrose gradient centrifugation, and single particle analysis (6Dudkina N.V. Eubel H. Keegstra W. Boekema E.J. Braun H.P. Proc. Natl. Acad. Sci. U.S.A. 2005; 102: 3225-3229Crossref PubMed Scopus (263) Google Scholar, 7Schäfer E. Dencher N.A. Vonck J. Parcej D.N. Biochemistry. 2007; 46: 12579-12585Crossref PubMed Scopus (134) Google Scholar). A recent study by Acin-Perez et al. (8Acín-Pérez R. Fernández-Silva P. Peleato M.L. Pérez-Martos A. Enriquez J.A. Mol. Cell. 2008; 32: 529-539Abstract Full Text Full Text PDF PubMed Scopus (568) Google Scholar) convincingly showed that supercomplexes are functional units capable of consuming oxygen when provided appropriate electron donors. They concluded that supercomplexes are in fact the functional respiratory unit of the mitochondrion in vivo. Schagger and Pfeiffer (9Schägger H. Pfeiffer K. EMBO J. 2000; 19: 1777-1783Crossref PubMed Scopus (1013) Google Scholar) demonstrated that supercomplex I·III·IV appears on blue native gels (BNGs) with increasing stoichiometries of complex IV. They termed these entities S0–S4, where the numeral denotes the number of complex IVs within the supercomplex.Supercomplexes provide a logical explanation for combined deficiencies of the electron transport chain (ETC) observed in patients. It is estimated that ∼30% of all ETC disorders involve multiple complexes (10Smits P. Mattijssen S. Morava E. van den Brand M. van den Brandt F. Wijburg F. Pruijn G. Smeitink J. Nijtmans L. Rodenburg R. van den Heuvel L. Eur. J. Hum. Genet. 2010; 18: 324-329Crossref PubMed Scopus (28) Google Scholar). Combined I·IV deficiencies (11Benecke R. Strümper P. Weiss H. Brain. 1993; 116: 1451-1463Crossref PubMed Scopus (190) Google Scholar, 12Brass E.P. Hiatt W.R. Gardner A.W. Hoppel C.L. Am. J. Physiol. Heart Circ. Physiol. 2001; 280: H603-H609Crossref PubMed Google Scholar, 13Korenke G.C. Bentlage H.A. Ruitenbeek W. Sengers R.C. Sperl W. Trijbels J.M. Gabreels F.J. Wijburg F.A. Wiedermann V. Hanefeld F. et al.Eur. J. Pediatr. 1990; 150: 104-108Crossref PubMed Scopus (25) Google Scholar, 14van Straaten H.L. van Tintelen J.P. Trijbels J.M. van den Heuvel L.P. Troost D. Rozemuller J.M. Duran M. de Vries L.S. Schuelke M. Barth P.G. Neuropediatrics. 2005; 36: 193-199Crossref PubMed Scopus (29) Google Scholar), as well as multiple examples of combined I·III deficiencies have been reported (15Schägger H. de Coo R. Bauer M.F. Hofmann S. Godinot C. Brandt U. J. Biol. Chem. 2004; 279: 36349-36353Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar, 16Budde S.M. van den Heuvel L.P. Janssen A.J. Smeets R.J. Buskens C.A. DeMeirleir L. Van Coster R. Baethmann M. Voit T. Trijbels J.M. Smeitink J.A. Biochem. Biophys. Res. Commun. 2000; 275: 63-68Crossref PubMed Scopus (162) Google Scholar, 17Lamantea E. Carrara F. Mariotti C. Morandi L. Tiranti V. Zeviani M. Neuromuscul. Disord. 2002; 12: 49-52Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar). In most eukaryotes, complex III is composed of 11 subunits (18Iwata S. Lee J.W. Okada K. Lee J.K. Iwata M. Rasmussen B. Link T.A. Ramaswamy S. Jap B.K. Science. 1998; 281: 64-71Crossref PubMed Scopus (1055) Google Scholar, 19Xia D. Yu C.A. Kim H. Xia J.Z. Kachurin A.M. Zhang L. Yu L. Deisenhofer J. Science. 1997; 277: 60-66Crossref PubMed Scopus (867) Google Scholar), of which only cytochrome b is encoded by the mitochondrial genome. The catalytic core of complex III is comprised of cytochrome b, ISP (iron sulfur protein; Rieske protein), and cytochrome c1. Most of the mutations in cytochrome b cause isolated complex III deficiencies. However, there is a subset of cytochrome b mutations that cause combined I·III deficiencies, both in patients (15Schägger H. de Coo R. Bauer M.F. Hofmann S. Godinot C. Brandt U. J. Biol. Chem. 2004; 279: 36349-36353Abstract Full Text Full Text PDF PubMed Scopus (254) Google Scholar, 16Budde S.M. van den Heuvel L.P. Janssen A.J. Smeets R.J. Buskens C.A. DeMeirleir L. Van Coster R. Baethmann M. Voit T. Trijbels J.M. Smeitink J.A. Biochem. Biophys. Res. Commun. 2000; 275: 63-68Crossref PubMed Scopus (162) Google Scholar, 17Lamantea E. Carrara F. Mariotti C. Morandi L. Tiranti V. Zeviani M. Neuromuscul. Disord. 2002; 12: 49-52Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar, 20Blakely E.L. Mitchell A.L. Fisher N. Meunier B. Nijtmans L.G. Schaefer A.M. Jackson M.J. Turnbull D.M. Taylor R.W. FEBS J. 2005; PubMed Scopus Google Scholar) and in R. Fernández-Silva P. R. Pérez-Martos A. C. J.A. Mol. Cell. 2004; Full Text Full Text PDF PubMed Scopus Google Scholar). In of cytochrome has been reported to to of both complexes I and IV in J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). these has been that assembled complex III, functional or is for the assembly and of complex mutations in ISP or cytochrome have been reported in However, complex III deficiencies in patients are by mutations in E. M. P. Carrara F. L. E. A. G. Zeviani M. Hum. Mol. Genet. 2007; PubMed Scopus Google Scholar, P. A. M. A. J.W. E. D. N. A. de P. A. P. A. Genet. 2001; PubMed Scopus Google Scholar, L. S. E. B. A. E. W. Van Coster R. Am. J. Genet. A. PubMed Scopus Google Scholar), a of ISP in the complex III K. H. W. EMBO J. 18: PubMed Scopus Google Scholar, A. EMBO J. PubMed Scopus Google Scholar). are that in complex III the function of assembled complex I without decreasing the amount of complex Caenorhabditis complex III a in the of and J. F. S. Cell. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar) reported that oxygen to oxygen and A in a complex III cytochrome b, was as a of a of an in the of with J. F. S. Cell. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). However, the cause of this is show that a of complex III, by a in the amount of assembled complex I without a in the amount of assembled complex III. we that ctb-1 complex I function without decreasing either the amount of assembled complex I or the of complex I in supercomplexes. In we show that the of with not from complex III function. on complex I from the of a into complex III. In this the of supercomplex that the of supercomplexes is on The of complex I and III in a model that supercomplexes a role in enzymatic of complexes I and III. The of the between of the ETC has for the of patients with in multiple