Early evolution of cytochrome bc complexes

Primary structures, functional characteristics and phylogenetic relationshi ps of subunits of cytochrome bc complexes from phylogenetically diverse bac terial and archaeal species were analysed. A single case of lateral gene tr ansfer, i.e. the import of an epsilon-proteobacterial cytochrome bc(1) comp lex into Aquificales, was identified. For the enzyme in the remainder of th e species studied, the obtained phylogenies were globally in line with smal l subunit rRNA trees. The distribution of a few key phylogenetic markers, s uch as contiguousness of cytochrome b, nature of the c-type subunit or spac ing between b-heme Ligands, are discussed. A localised modification of prev ious tree topologies is proposed on the basis of the obtained data. The com parison of extant enzymes furthermore allowed us to define the minimal func tional and evolutionary core of the enzyme. The data furthermore suggest th at the ancestral enzyme was put together from subunits that previously had played a role in other electron transfer chains. (C) 2000 Academic Press.