Discovery of Multiple Modified F 430 Coenzymes in Methanogens and Anaerobic Methanotrophic Archaea Suggests Possible New Roles for F 430 in Nature

Abstract

ABSTRACT Methane is a potent greenhouse gas that is generated and consumed in anaerobic environments through the energy metabolism of methanogens and an aerobic me thanotrophic archaea (ANME), respectively. Coenzyme F 430 is essential for methanogenesis, and a structural variant of F 430 , 17 2 -methylthio-F 430 (F 430 -2), is found in ANME and is presumably essential for the anaerobic oxidation of methane. Here we use liquid chromatography–high-resolution mass spectrometry to identify several new structural variants of F 430 in the cell extracts of selected methanogens and ANME. Methanocaldococcus jannaschii and Methanococcus maripaludis contain an F 430 variant (denoted F 430 -3) that has an M + of 1,009.2781. This mass increase of 103.9913 over that of F 430 corresponds to C 3 H 4 O 2 S and is consistent with the addition of a 3-mercaptopropionate moiety bound as a thioether followed by a cyclization. The UV absorbance spectrum of F 430 -3 was different from that of F 430 and instead matched that of an F 430 derivative where the 17 3 keto moiety had been reduced. This is the first report of a modified F 430 in methanogens. In a search for F 430 -2 and F 430 -3 in other methanogens and ANME, we have identified a total of nine modified F 430 structures. One of these compounds may be an abiotic oxidative product of F 430 , but the others represent naturally modified versions of F 430 . This work indicates that F 430 -related molecules have additional functions in nature and will inspire further research to determine the biochemical role(s) of these variants and the pathways involved in their biosynthesis.