Kristallstrukturen von F420-abhängiger Alkohol-Dehydrogenase (Adf) und F420-abhängiger Methylentetrahydromethanopterin-Reduktase (Mer)

Coenzyme binding in F420-dependent secondary alcohol dehydrogenase, a member of the bacterial luciferase family F420-dependent secondary alcohol dehydrogenase (Adf) from methanogenic archaea is a member of the growing bacterial luciferase family which are all TIM barrel enzymes, most of which with an unusual non-prolyl cis-peptide bond. In addition to the structurally characterized FMN dependent luciferase (LuxAB) from bacteria and F420-dependent methylenetetrahydromethanopterin reductase (Mer) from methanogenic archaea, the F420-dependent glucose-6-phosphate dehydrogenase from Mycobacteria also belongs to this family. The crystal structure of Adf from Methanoculleus thermophilicus was solved at 1.8 Å resolution in complex with an F420-acetone adduct. F420 is embedded into a cavity located at the C-terminal end of the barrel. The knowledge of the F420 binding mode in Adf provides the molecular basis for modelling F420 and FMN into the other enzymes of the family. A non-prolyl cis-peptide bond also present in Mer and LuxAB was identified as an essential part of a bulge that serves as backstop at the Re-face of F420 to keep it in a bent conformation. The acetone moiety of the F420-acetone adduct is positioned at the Si-face of F420 deeply buried inside the protein. Isopropanol can be reliably modelled and a hydrogen transfer mechanism postulated on the assumption that the isopropanol hydroxyl group sits in the same position as the acetone oxygen. His39 and Glu108 can be identified as key players for binding of the acetone or isopropanol oxygen and for catalysis. Recently, we solved the structure of Mer from Methanosarcina barkeri in complex with F420. A catalytical mechanism of Mer based on molecular modeling studies will be discussed in this context.