Physiology and Bioenergetics of [NiFe]-Hydrogenase 2-Catalyzed H2-Consuming and H2-Producing Reactions in Escherichia coli

Abstract

Escherichia coliuptake hydrogenase 2 (Hyd-2) catalyzes the reversible oxidation of H2to protons and electrons. Hyd-2 synthesis is strongly upregulated during growth on glycerol or on glycerol-fumarate. Membrane-associated Hyd-2 is an unusual heterotetrameric [NiFe]-hydrogenase that lacks a typical cytochromebmembrane anchor subunit, which transfers electrons to the quinone pool. Instead, Hyd-2 has an additional electron transfer subunit, termed HybA, with four predicted iron-sulfur clusters. Here, we examined the physiological role of the HybA subunit. During respiratory growth with glycerol and fumarate, Hyd-2 used menaquinone/demethylmenaquinone (MQ/DMQ) to couple hydrogen oxidation to fumarate reduction. HybA was essential for electron transfer from Hyd-2 to MQ/DMQ. H2evolution catalyzed by Hyd-2 during fermentation of glycerol in the presence of Casamino Acids or in a fumarate reductase-negative strain growing with glycerol-fumarate was also shown to be dependent on both HybA and MQ/DMQ. The uncoupler carbonyl cyanidem-chlorophenylhydrazone (CCCP) inhibited Hyd-2-dependent H2evolution from glycerol, indicating the requirement for a proton gradient. In contrast, CCCP failed to inhibit H2-coupled fumarate reduction. Although a Hyd-2 enzyme lacking HybA could not catalyze Hyd-2-dependent H2oxidation or H2evolution in whole cells, reversible H2-dependent reduction of viologen dyes still occurred. Finally, hydrogen-dependent dye reduction by Hyd-2 was reversibly inhibited in extracts derived from cells grown in H2evolution mode. Our findings suggest that Hyd-2 switches between H2-consuming and H2-producing modes in response to the redox status of the quinone pool. Hyd-2-dependent H2evolution from glycerol requires reverse electron transport.