Investigating the production of coenzyme F 430 variants in methanogenic archaea

Abstract

Methanogenesis is the biological production of methane and is utilized by methanogenic archaea (methanogens) as a form of anaerobic respiration to generate energy. Methanogens are found in virtually any anaerobic environment and are responsible for over 70% of total atmospheric methane, a greenhouse gas 84 times more potent than carbon dioxide over a twenty-year period. Due to the abundance of methane and its powerful heat-trapping capability, it is among the most significant greenhouse gases. In addition to methane's importance as a greenhouse gas, it is a valuable and clean energy source that emits 50% less carbon dioxide than coal combustion. An attractive possibility for further exploiting the chemical energy stored in methane is to convert it to more useable liquid fuels and other value-added chemicals. This could be accomplished by producing a methanogenic strain capable of reversing methanogenesis and converting methane to methanol. Before this can be realized, however, the chemistry of methanogenesis must be more fully understood. The final, rate-determining, methane-forming step of methanogenesis is catalyzed by methyl-coenzyme M reductase (MCR) and its prosthetic group, cofactor F430, a unique nickel-containing tetrapyrrole that is the essential catalytic component of MCR. Recently, multiple F430 variants have been discovered in several methanogenic species, including the two model methanogens Methanococcus maripaludis and Methanosarcina acetivorans. Our research suggests that one of these variants, mercaptopropionate-F430, (F430-3) is produced by M. maripaludis almost exclusively in stationary phase of growth, suggesting that nutrient deprivation induces the production of this variant. We hypothesize that hydrogen deprivation is involved in inducing this expression, but future experiments will be conducted to confirm this. We further have implicated a likely enzyme involved in the first step of F430-3 biosynthesis, the insertion of a sulfur atom. This research sets the stage for further investigation into how these two variants modulate MCR catalysis.