Our research is focussed on structural biology primarily based on X-ray crystallography as a method for structure determination. We are predominantly interested in proteins involved in the (anaerobic) degradation of biomass, in particular, on those of methanogenic, fermenting and inert aliphatic and aromatic hydrocarbon metabolising pathways. The investigated enzymes catalyse challenging biochemical reactions with novel mechanisms, chemically driven ion-translocations across the cell membrane and flavin-based electron bifurcation processes in which the production of energy-rich reduced ferredoxins is coupled with exergonic reduction reactions. Furthermore, we are, in general, interested in the structure of (unusual) organic or metallic cofactors, their formation, and their function in cooperation with the polypeptide. As an example, four protein structures are given in the figure on the left.