This is one of three E.coli hydrogenases synthesized in response to different physiological conditions. HYD2 is involved in hydrogen uptake. A + H2 = AH2 Binds 1 [3Fe-4S] cluster. Binds 2 [4Fe-4S] clusters. Heterodimer of a large and a small subunit. Exported by the Tat system. The position of the signal peptide cleavage has been experimentally proven. Can also be exported by the Sec system. Belongs to the [NiFe]/[NiFeSe] hydrogenase small subunit family.