Involved in the biosynthesis of tetrahydromethanopterin, a coenzyme used in methanogenesis. Catalyzes the reduction of dihydromethanopterin (H(2)MPT) to tetrahydromethanopterin (H(4)MPT). Ferredoxin may serve as an electron donor. 5,6,7,8-tetrahydromethanopterin + A = 7,8-dihydromethanopterin + AH2 Binds 2 [4Fe-4S] clusters per subunit. Cofactor biosynthesis; 5,6,7,8-tetrahydromethanopterin biosynthesis. Homodimer.