Comparative genomics reveals electron transfer and syntrophic mechanisms differentiating methanotrophic and methanogenic archaea
Fig 7
Depiction of the primary structure of HdrA and the quaternary structure of the HdrABC-MvhADG complex based on the structure from M. wolfeii. (A) HdrA can be broken down into 4 domains, the positions of these domains and key iron–sulfur cluster binding cysteines are illustrated, scale denotes amino acid position in the M. wolfeii sequence. (B) Quaternary structure of the entire HdrABC-MvhABG complex illustrating the dimeric structure. Metal cofactors involved in the oxidation/reduction of substrates or electron transport through the complex are highlighted. (C) Detail of HdrA domain structure highlighting cofactor position and proposed electron flow from MvhD in through the C-terminal ferredoxin, bifurcation through the FAD cofactor, with 2 electrons flowing out through HdrBC via the thioredoxin reductase domain’s FeS cluster, while 2 other electrons flow out through the inserted ferredoxin domain, presumably to free ferredoxin (Fd2−). Importantly, for the proposed heterodimeric HdrA discussed here, this latter electron flow passes through the FeS cluster bound through a combination of Cys residues in the N-terminal domain, combined with a single Cys from the other HdrA subunit (Cys197 highlighted in red). FAD, flavin adenine dinucleotide.