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). coenzyme B + coenzyme M + 2 H(+) + 2 reduced [2Fe-2S]-[ferredoxin] = coenzyme M-coenzyme B heterodisulfide + 2 H2 + 2 oxidized [2Fe-2S]-[ferredoxin] 2 CO2 + coenzyme B + coenzyme M + 2 reduced [2Fe-2S]-[ferredoxin] = coenzyme M-coenzyme B heterodisulfide + 2 formate + 2 oxidized [2Fe-2S]-[ferredoxin] Cofactor metabolism; coenzyme M-coenzyme B heterodisulfide reduction; coenzyme B and coenzyme M from coenzyme M-coenzyme B heterodisulfide: step 1/1. The heterodisulfide reductase is composed of three subunits; HdrA, HdrB and HdrC. B1 and B2 subunits are interchangeable, as are the C1 and C2 subunits. The heterodisulfide reductase forms a supercomplex with formylmethanofuran dehydrogenase (Fwd), F(420)-non-reducing hydrogenase (Vhu) and formate dehydrogenase (Fdh). Belongs to the HdrB family.