Part of a complex that catalyzes the reversible reduction of CoM-S-S-CoB to the thiol-coenzymes H-S-CoM (coenzyme M) and H-S-CoB (coenzyme B). Probably involved in methylotrophic methanogenesis but not in aceticlastic methanogenesis. coenzyme B + coenzyme M + 2 oxidized [2Fe-2S]-[ferredoxin] = coenzyme M-coenzyme B heterodisulfide + 2 H(+) + 2 reduced [2Fe-2S]-[ferredoxin] Binds 4 [4Fe-4S] cluster. Cofactor metabolism; coenzyme M-coenzyme B heterodisulfide reduction; coenzyme B and coenzyme M from coenzyme M-coenzyme B heterodisulfide: step 1/1. The ferredoxin:CoB-CoM heterodisulfide reductase is composed of three subunits; HdrA1, HdrB1 and HdrC1. Induced on trimethylamine or methanol, but not on acetate as the sole energy source. Triple hdrA1C1B1 deletion decreases methane production from methanol, but does not affect methanogenesis from acetate. Deletion results in up-regulation of CoB-SH and CoM-SH synthesis and transport, and methylsulfide methyltransferases. Belongs to the HdrA family.