Molybdenum-containing enzymes: Molybdenum is the only second-row transition metal that is required by most living organisms. The few species that do not require molybdenum use tungsten, which lies immediately below molybdenum on the periodic table. Because of its unique chemical versatility and unusually high bioavailability molybdenum has been incorporated into the active sites of enzymes over the course of evolution. These enzymes are found in all domains of life, participating in fundamental biological processes.
Interestingly, microbes which respire with an incredibly diverse range of substrates (such as nitrate (or nitrite), S-oxides, N-oxides, (per)chlorate, selenate, arsenate (or arsenite), dimethylsulfide and formate) all use molybdenum-containing enzymes as terminal reductases/dehydrogenases. We are particularly interested in issues of structural-based substrate specificity for this group of enzymes. To this end we are working on three molybdoenzymes: the selenate reductase from Thauera selenatis, the arsenite oxidase from the bacterium termed NT-14 and the DMS dehydrogenase from Rhodovulum sulfidophilum. Based on sequence comparisons, all three enzymes belong to the DMSO reductase family of molybdoenzymes.
We aim to solve the structure of all three enzymes by X-ray crystallography and examine the structures of their active sites in detail using X-ray absorption spectroscopy. This information will assist in understanding the structural basis of their substrate specificities and reaction mechanisms. Engineering of the selenate- and arsenite-utilizing enzymes may lead to applications in bioremediation.