H2 + NAD(+) = H(+) + NADH Binds 2 [4Fe-4S] clusters. Binds 1 [3Fe-4S] cluster. Binds 1 [2Fe-2S] cluster. Tetramer of an alpha and a gamma subunits (flavin-containing dimer), and a delta and a nickel-containing beta subunits (hydrogenase dimer). Belongs to the [NiFe]/[NiFeSe] hydrogenase small subunit family.