P4

Hans-Georg Koch / Petra Hellwig (Strasbourg)

Assembly of cytochrome cbb₃-type Cytochrome oxidases

Heme-copper oxidases are universally conserved integral multisubunit membrane proteins that catalyze the terminal reaction of respiratory electron transport chains in mitochondria and aerobic bacteria. Bacterial respiratory chains usually contain multiple terminal oxidases, which allow bacteria to adapt to different environmental O₂ concentrations during their life cycle. The ability to cope with low oxygen concentrations is in particular important for pathogenic bacteria, which colonize human tissues of low oxygen concentration, like the intestine.  Many of these bacteria like Helicobacter pylori, Vibrio cholerae or Campylobacter jejuni, contain a special kind of heme-copper oxidase, the cbb₃-type Cytochrome oxidase. The major advantage of this enzyme is that its oxygen affinity is significantly higher than the oxygen affinity of the mitochondrial-type aa₃-type Cytochrome oxidase. The frequent occurrence of cbb­₃-type oxidases in pathogenic bacteria has raised the question of whether cbb₃-type oxidases and their specific assembly factors are important determinants of pathogenicity.

The characteristic subunit composition and cofactor content of cbb₃ type oxidases in comparison to aa₃ type oxidases, suggests a specific assembly pathway with dedicated assembly factors. The temporal and spatial dissection of the cbb₃ oxidase assembly pathway offers the opportunity to specifically interfere with cbb₃ oxidase assembly without affecting the aa₃ oxidase in the human host. Indeed, we have identified several assembly proteins which are required for cbb₃-type oxidase assembly, but which are not involved in aa₃ type oxidase assembly. The exact function of these assembly factors need to be determined at a molecular level and their potential to develop into a drug target need to be explored.

We employ a wide range of highly relevant and sophisticated methods, including: in vitro transcription/translation systems; chemical and site directed cross-linking; BN-PAGE and 2D-PAGE; Spectroscopic analyses (in collaboration with P. Hellwig, University Straßburg); in vivo FRET analyses (in collaboration with P. Graumann, University Freiburg & I. Schalk, ESBS Straßburg)

→to the Koch group website

→to the Hellwig group website

Selected Publications:

1. Kulajta, C., Thumfart, J., Haid, S., Daldal, F. and Koch, H.-G. (2006). Multi-step assembly pathway of the cbb₃-type cytochrome c oxidase complex. J. Mol. Biol. 355, 989-1004.

2. Aygun-Sunar, S., Mandaci, S., Koch, H.-G., Murray, I.V.J., Goldfine, H. and Daldal, F. (2006). Ornithine lipid is required for optimal steady-state amounts of c-type cytochromes in Rhodobacter capsulatus.  Mol.  Microbiol. 61, 418-435.

3. Koch, H.-G. and Schneider, D (2007) Folding, assembly and stability of transmembrane cytochromes. Current Chemical Biology 1; 59-74

4. Sanders, C., Turkarsalan, S., Onder, O., Frawley, E.R., Kranz, R.G., Koch, H.-G. and Daldal, F., (2008) Biogenesis of c-type cytochromes and cytochrome complexes. In: Advances in Photosynthesis and Respiration (Govindjee, Hrsg), Springer Verlag, Berlin, in press