Identification and Biosynthesis of 1‑Mercaptoethanesulfonic Acid (1-MES), an Analogue of Coenzyme M, Found Widely in the Methanogenic Archaea

Here I report on the identification of 1-mercaptoethanesulfonic acid (1-MES), an analogue of 2-mercaptoethanesulfonic acid (coenzyme M, HSCoM). 1-MES and HSCoM were both present in the growth media of eight different methanogens at concentrations ranging from ∼1 to 100 μM. In an effort to determine a chemical origin of 1-MES, several plausible chemical routes were examined each assuming that HSCoM was the precursor. In all examined routes, no 1-MES was formed. However, 1-MES was formed when a solution of vinylsulfonic acid and sulfide were exposed to ultraviolet light. On the basis of these results, I conclude 1-MES is formed enzymatically. This was confirmed by growing a culture of Methanococcus maripaludis S2 in the presence of [1,1′,2,2′-2H4]­HSCoM and measuring the incorporation of deuterium into 1-MES. 1-MES incorporated three of the four deuteriums from the fed HSCoM. This result is consistent with the abstraction of a C-2 deuterium of the HSCoM, likely by a 5′-dAdoCH2 • radical, followed by a radical rearrangement in which the sulfonic acid moves to position C-1, followed by abstraction of a H• likely from 5′-dAdoCH2D. At present, the reason for the production of 1-MES is not clear. This is the first report of the occurrence of 1-MES in Nature.