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bioRxiv · 10.1101/2022.02.02.478877

Structure-based electron-confurcation mechanism of the Ldh-EtfAB complex

Ermler, U.·Kayastha, K.·Katsyv, A.·Himmrichs, C.·Welsch, S.·Schuller, J. M.·Müller, V.
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Abstract

Lactate oxidation with NAD+ as electron acceptor is a highly endergonic reaction and some anaerobic bacteria overcome the energetic hurdle by flavin-based electron bifurcation/confurcation (FBEB/FBEC) using a lactate dehydrogenase (Ldh) in concert with the electron transferring proteins EtfA and EtfB. The electron cryo-microscopically (cryo-EM) characterized (Ldh-EtfAB)2 complex of Acetobacterium woodii at 2.43 [A] resolution consists of a mobile EtfAB shuttle located between the rigid central Ldh and the peripheral EtfAB base units. The FADs of Ldh and the EtfAB shuttle contact each other thereby forming the D (dehydrogenase conducting) state. The intermediary Asp37 and Asp139 may harmonize the redox potentials between the FADs and the pyruvate/lactate pair crucial for FBEC. A plausible novel B (bifurcation conducting) state with the EtfAB base and shuttle FADs in a productive electron transfer distance was derived by integrating Alphafold2 calculations. Kinetic analysis of enzyme variants shed light on the connection between NAD binding/release and D-to-B state transition. The FBEC inactivity when truncating the ferredoxin domain of EtfA substantiates its role as redox relay. Lactate oxidation in Ldh is based on the catalytic base His423 and a metal center. On this basis, a comprehensive catalytic mechanism of the FBEC process was outlined.

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Ermler, U., Kayastha, K., Katsyv, A., Himmrichs, C., Welsch, S., Schuller, J. M., Müller, V.. 2022-02-03. Structure-based electron-confurcation mechanism of the Ldh-EtfAB complex. https://doi.org/10.1101/2022.02.02.478877

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