A Soluble NADH-Dependent Fumarate Reductase in the Reductive Tricarboxylic Acid Cycle of Hydrogenobacter thermophilus TK-6

Abstract

Fumarate reductase (FRD) is an enzyme that reduces fumarate to succinate. In many organisms, it is bound to the membrane and uses electron donors such as quinol. In this study, an FRD from a thermophilic chemolithoautotrophic bacterium, Hydrogenobacter thermophilus TK-6, was purified and characterized. FRD activity using NADH as an electron donor was not detected in the membrane fraction but was found in the soluble fraction. The purified enzyme was demonstrated to be a novel type of FRD, consisting of five subunits. One subunit showed high sequence identity to the catalytic subunits of known FRDs. Although the genes of typical FRDs are assembled in a cluster, the five genes encoding the H. thermophilus FRD were distant from each other in the genome. Furthermore, phylogenetic analysis showed that the H. thermophilus FRD was located in a distinct position from those of known soluble FRDs. This is the first report of a soluble NADH-dependent FRD in Bacteria and of the purification of a FRD that operates in the reductive tricarboxylic acid cycle.

Ecological Aspects of the Distribution of Different Autotrophic CO 2 Fixation Pathways

“…Although the native electron donor for fumarate reductase in Chlorobium is not known, it was shown to be NADH in Hydrogenobacter (72). The cycle requires (at least in Chlorobium) only two ATP equivalents to form pyruvate (and three additional ATPs to convert it to triosephosphates) and is therefore less energy-consuming than the CB cycle.…”

Combining reverse genetics and nuclear magnetic resonance‐based metabolomics unravels trypanosome‐specific metabolic pathways

“…Indeed, inclusion of the glycosomal succinate branch in the procyclic trypanosomes releases PEP molecules used to produce ATP in the cytosol through pyruvate kinase activity, which has been described as essential for the viability of the procyclic form (Morris et al, 2002;Coustou et al, 2003;Deramchia et al, 2014). The trypanosome FRD enzymes were the first soluble NADH-dependent FRD characterized, although the concept might be more widely applicable as soluble NADH-dependent FRD activity was reported in the parasite Trichomonas foetus (Müller, 2003) and the prokaryote Hydrogenobacter thermophilus (Miura et al, 2008).…”

Identification of Missing Genes and Enzymes for Autotrophic Carbon Fixation in Crenarchaeota

“…The search of the I. hospitalis genome resulted in two genes, Igni_0276 and Igni_0445 (24). Recently, a soluble, five-component, NADHdependent fumarate reductase was identified in Hydrogenobacter thermophilus (38) that operates in the reductive citric acid cycle. The fumarate reductase subunit A (HTH_1421) shows high similarity to Tneu_0423 and Igni_0276 (43 and 60% and 50 and 67% aa identity/similarity), whereas the subunit B (HTH_0983) has lower similarity to Tneu_0424 and Igni_0445 (37 and 56% and 29 and 50% aa identity and similarity, respectively).…”