PARENT SESSION

Symposium S8A Cytochrome b-c complexes
Friday September 3rd, 2004 8:30 AM-10:30 AM Room 511D
Chair: Fevzi Daldal
Co-Chair: David Kramer

Cytochrome c₁ is a collapsed di-heme cytochrome. Frauke Baymann^*,, Evelyne Lebrun, Wolfgang Nitschke,

ABSTRACT- Cytochrome c₁ from the cytochrome bc₁ complex of mitochondria and -, -,and -proteobacteria and and the di-heme cytochromes c in the corresponding enzyme from -proteobacteria were so far considered to represent unrelated cytochromes. A missing link protein discovered in the genome of the hyperthermophilic bacterium Aquifex aeolicus, however, provides evidence for a close evolutionary relationship between these two cytochromes. The mono-heme cytochrome c₁ from Aquifex aeolicus contains stretches of strong sequence homology towards the -proteobacterial di-heme cytochromes. These di-heme cytochromes are shown to belong to the cytochrome c₄ family. Mapping cytochrome c₁ onto the diheme sequences and structures demonstrates that cytochrome c₁ results from a mutation-induced collapse of the di-heme cytochrome structure and provides an explanation for its uncommon structural features. The appearance of cytochrome c₁ thus represents an extension of the biological protein repertoire quite different from the widespread innovation by gene duplication and subsequent diversification.

KEY WORDS: evolution, lateral gene transfer, bc1-complex, structure