Structural basis for methylphosphonate biosynthesis

A source of methane in the upper ocean Methane concentrations are high in oxygenated surface waters. Methylphosphonate (MPn) is a suggested source, but an enzyme that synthesizes Mpn (MPnS) has so far only been identified in one ocean microbe, albeit an abundant one: the archaeon Nitrosopumilus maritimus . Born et al. describe the crystal structure of MPnS and of a related enzyme that acts on the same substrate but makes a different product. By comparing the structures, they determined sequence markers that allowed them to identify MPnS in other ocean microbes, including the abundant microbe Pelagibacter ubique . These findings support the proposal that MPn is a source of both methane and phosphorus in the upper aerobic ocean. Science , this issue p. 1336