Identification of the Radical SAM Enzymes Involved in the Biosynthesis of Methanopterin and Coenzyme F 420 in Methanogens.

Methanogenic archaea represent a source of unique and fascinating anaerobic biochemistry that includes the involvement of many radical S-adenosyl-l-methionine (SAM) enzymes, some of which have well-established functions, while the majority have currently unknown or only partially understood functions. Here, we describe our strategy for the identification of the radical SAM enzyme that catalyzes the two methylation reactions in methanopterin biosynthesis in Methanocaldococcus jannaschii. Additionally, we describe the similar strategy carried out for the identification of the two radical SAM enzymes required for the biosynthesis of the 7,8-didemethyl-8-hydroxy-5-deazariboflavin (F0 ) moiety of coenzyme F420 in M. jannaschii. This approach can be employed for future functional identification of radical SAM enzymes with currently unknown functions.