Structural basis for the interaction of the chaperone Cbp3 with newly synthesized cytochrome b during mitochondrial respiratory chain assembly

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Assembly of the mitochondrial respiratory chain requires the coordinated synthesis of mitochondrial and nuclear encoded subunits, redox co-factor acquisition, and correct joining of the subunits to form functional complexes. The conserved Cbp3-Cbp6 chaperone complex binds newly synthesized cytochrome b and supports the ordered acquisition of the heme co-factors. Moreover, it functions as a translational activator by interacting with the mitoribosome. Cbp3 consists of two distinct domains, an N-terminal domain present in mitochondrial Cbp3 homologs, and a highly conserved C-terminal domain comprising a ubiquinol-cytochrome c chaperone region. Here, we solved the crystal structure of this C-terminal domain from a bacterial homolog at 1.4 Å resolution, revealing a unique all-helical fold. This structure allowed mapping of the interaction sites of yeast Cbp3 with Cbp6 and cytochrome b via site-specific photo-crosslinking. We propose that mitochondrial Cbp3 homologs carry an N-terminal extension that positions the conserved C-terminal domain at the ribosomal tunnel exit for an efficient interaction with its substrate, the newly synthesized cytochrome b protein.


  • Mama Ndi
  • Geoffrey Masuyer
  • Hannah Dawitz
  • Andreas Carlström
  • Mirco Michel
  • Arne Elofsson
  • Mikaela Rapp
  • Pål Stenmark
  • Martin Ott
External organisations
  • Karolinska University Hospital
  • Stockholm University
Original languageEnglish
JournalJournal of Biological Chemistry
Publication statusE-pub ahead of print - 2019 Sep 19
Publication categoryResearch
Externally publishedYes

Bibliographic note

Published under license by The American Society for Biochemistry and Molecular Biology, Inc.