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= Formylmethanofuran Dehydrogenase = FIRST 250 WORDS

Biological Occurrence
Romesser and Wolfe were able to find molybdenum-containing formylmethanofuran dehydrogenase from Methanosarcina barkeri and Archaeoglobus fulgidus cell extracts. Additionally, Wolfe and Donnelly suggested that Methanobacterium thermoautotrophicum contains molybdenum and tungsten formylmethanofuran dehydrogenase because it catalyzes the oxidation of formylmethanofuran to methanofuran and carbon dioxide. Wagner, Ermler, and Shima also purified molybdenum-containing formylmethanofuran dehydrogenase from Methanothermobacter wolfeii.

Structure
In 2016, the X-ray structure of formylmethanofuran dehydrogenase was determined. The formylmethanofuran dehydrogenase contains multiple iron-sulfur cubane clusters and two heterohexamers FwdABCDFG. The two FwdABCDFG heterohexamers are arranged in a way that they are like a mirror-image of one another and the iron-sulfur clusters are found scattered in the middle of the two heterohexamers. The subunit FwdA contains zinc ligands while FwdF is composed of four T-shaped ferrodoxin domains that are similar. FwdBD has a redox-active tungsten. The tungsten in FwdBD is coordinated by four dithiolene thiolates. Six sulfurs coordinate to the tungsten of tungstopterin at the active site of FwdB. The tungsten is coordinated in a distorted octahedral geometry. A carbon dioxide (CO2) suitable binding site is occupied by the solvent. The binding site lies between Cys118, His119, Arg228, and sulfur-tungsten ligand.

Methanogenesis Catalyzation
Formylmethanofuran dehydrogenase catalyzes the methanogenesis reaction by reducing carbon dioxide (CO2) instead of bicarbonate to form carboxyformylmethanofuran. The structural data obtained from the X-ray structure suggests that carbon dioxide (CO2) is reduced to formate by ferredoxin at the tungstopterin active site in FwdBD. Then, it reduces the carboxyformylmethanofuran to formylmethanofuran at its tungsten or molybdenum active site.