title: The Cbp3-Cbp6 complex coordinates cytochrome b synthesis with bc(1) complex assembly in yeast mitochondria.
abstract: Respiratory chain complexes in mitochondria are assembled from subunits derived from two genetic systems. For example, the bc(1) complex consists of nine nuclear encoded subunits and the mitochondrially encoded subunit cytochrome b. We recently showed that the Cbp3-Cbp6 complex has a dual function for biogenesis of cytochrome b: it is both required for efficient synthesis of cytochrome b and for protection of the newly synthesized protein from proteolysis. Here, we report that Cbp3-Cbp6 also coordinates cytochrome b synthesis with bc(1) complex assembly. We show that newly synthesized cytochrome b assembled through a series of four assembly intermediates. Blocking assembly at early and intermediate steps resulted in sequestration of Cbp3-Cbp6 in a cytochrome b-containing complex, thereby making Cbp3-Cbp6 unavailable for cytochrome b synthesis and thus reducing overall cytochrome b levels. This feedback loop regulates protein synthesis at the inner mitochondrial membrane by directly monitoring the efficiency of bc(1) complex assembly.
authors.affiliation: Center for Biomembrane Research, Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden.
authors.forename: Steffi
authors.initials: S
authors.lastname: Gruschke
authors.forename: Katharina
authors.initials: K
authors.lastname: Römpler
authors.forename: Markus
authors.initials: M
authors.lastname: Hildenbeutel
authors.forename: Kirsten
authors.initials: K
authors.lastname: Kehrein
authors.forename: Inge
authors.initials: I
authors.lastname: Kühl
authors.forename: Nathalie
authors.initials: N
authors.lastname: Bonnefoy
authors.forename: Martin
authors.initials: M
authors.lastname: Ott
mesh_terms: D003573:Cytochrome b Group / Q000096:biosynthesis* / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: C435647:CBP3 protein, S cerevisiae; C561113:Cbp6 protein, S cerevisiae; D003573:Cytochrome b Group; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D018832:Molecular Chaperones; D029701:Saccharomyces cerevisiae Proteins