Characterization of NfnAB of Heliomicrobium modesticaldum, an Electron Bifurcating Enzyme Involved in Phototrophic Energy Conversion
Year: 2026
Type: article
Abstract: Analysis of the Heliomicrobium modesticaldum genome suggests that polypeptides encoded by the genes HM1_0289 and HM1_0290 correspond to the NfnA and NfnB subunits of an NAD-dependent ferredoxin:NADP + oxidoreductase electron-bifurcating enzyme, NfnAB, similar to that found in archea and anaerobic bacteria. NfnA contains a flavin cofactor and a [2Fe-2S] cluster, whose potential has not been previously measured. It exists in two spectroscopically distinct populations: a major species with E m ≈ -364 mV and a minor species with E m ≈ -423 mV. NfnB contains two [4Fe-4S] clusters, one with E m ≈ -430 mV and the other with E m ≤ -650 mV. Individually, NfnA and NfnB were selective for oxidation of NADH and NADPH respectively. Together, the NfnAB holoenzyme catalyzes the electron bifurcation reaction (2 Fd ox + NAD + + 2 NADPH ⇆ 2 Fd red + NADH + 2 NADP + ), where Fd corresponds to a heliobacterial dicluster ferredoxin. In the absence of a traditional FNR, heliobacteria may use NfnAB in electron confurcation to accomplish two functions: light-driven cyclic electron transport and transfer of reducing equivalents from NADH to NADP + . Deletion of the nfnAB genes resulted in mutants that were viable in all growth modes tested, but in vivo spectroscopic analysis indicated that light-driven electron transport was limited in the absence of NfnAB. As heliobacteria are considered descendants of a clostridial-type bacterium that received the genes for phototrophy via lateral gene transfer, NfnAB may be an archaic protein that was re-purposed for use in phototrophic energy conversion, a function not previously reported for this enzyme.
Source: Journal of Biological Chemistry
Institutions: Pennsylvania State University, Arizona State University
Language: English
Subfield: Biochemistry
Domain: Life Sciences
Open Access status: gold
Estimated APC paid: $3,430
Funder: Basic Energy Sciences
OpenAlex ID: W7223121240