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Publication Abstract from PubMed

NADH-dependent reduced ferredoxin: NADP oxidoreductase (NfnAB) is found in the cytoplasm of various anaerobic bacteria and archaea. The enzyme reversibly catalyzes the endergonic reduction of ferredoxin with NADPH driven by the exergonic transhydrogenation from NADPH onto NAD+. Coupling is most probably accomplished via the mechanism of flavin-based electron bifurcation. To understand this process on a structural basis we heterologously produced the NfnAB complex of Thermotoga maritima in E. coli, provided kinetic evidence for its bifurcating behavior and determined its X-ray structure in the absence and presence of NADH. The structure of NfnAB reveals an electron transfer route including the FAD (a-FAD) and the [2Fe-2S] cluster of NfnA and the FAD (b-FAD) and the two [4Fe-4S] clusters of NfnB. Ferredoxin is presumably docked onto NfnB close to the [4Fe-4S] cluster distal to b-FAD. NAD(H) binds to a-FAD and NADP(H) consequently to b-FAD which is positioned in the centre of the NfnAB complex and the site of electron bifurcation. Arg187 is hydrogen-bonded to N5 and O4 of the bifurcating b-FAD and might play a key role in adjusting a low redox potential of the FADH radical/FAD pair required for ferredoxin reduction. A mechanism of FAD-coupled electron bifurcation by NfnAB is proposed.

Insights into Flavin-based Electron Bifurcation via the NADH- dependent Reduced Ferredoxin: NADP oxidoreductase Structure.,Demmer JK, Huang H, Wang S, Demmer U, Thauer RK, Ermler U J Biol Chem. 2015 Jul 2. pii: jbc.M115.656520. PMID:26139605^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.