Elucidation of the biosynthesis of the methane catalyst coenzyme F₄₃₀

Methane biogenesis in methanogens is mediated by methyl-coenzyme M reductase, an enzyme that is also responsible for the utilization of methane through anaerobic methane oxidation. The enzyme uses an ancillary factor called coenzyme F₄₃₀, a nickel-containing modified tetrapyrrole that promotes catalysis through a methyl radical/Ni(ii)-thiolate intermediate. However, it is unclear how coenzyme F₄₃₀ is synthesized from the common primogenitor uroporphyrinogen iii, incorporating 11 steric centres into the macrocycle, although the pathway must involve chelation, amidation, macrocyclic ring reduction, lactamization and carbocyclic ring formation. Here we identify the proteins that catalyse the biosynthesis of coenzyme F₄₃₀ from sirohydrochlorin, termed CfbA-CfbE, and demonstrate their activity. The research completes our understanding of how the repertoire of tetrapyrrole-based pigments are constructed, permitting the development of recombinant systems to use these metalloprosthetic groups more widely.