Also known as MTRC_METM5, mtrC. Part of a complex that catalyzes the formation of methyl-coenzyme M and tetrahydromethanopterin from coenzyme M and methyl-tetrahydromethanopterin. This is an energy-conserving, sodium-ion translocating step. The complex is composed of 8 subunits; MtrA, MtrB, MtrC, MtrD, MtrE, MtrF, MtrG and MtrH.