How [FeFe]-Hydrogenase Facilitates Bidirectional Proton Transfer

Senger, M. and Eichmann, V. and Laun, K. and Duan, J. and Wittkamp, F. and Knör, G. and Apfel, U.-P. and Happe, T. and Winkler, M. and Heberle, J. and Stripp, S.T.

Volume: 141 Pages: 17394-17403
DOI: 10.1021/jacs.9b09225
Published: 2019

Hydrogenases are metalloenzymes that catalyze the conversion of protons and molecular hydrogen, H2. [FeFe]-hydrogenases show particularly high rates of hydrogen turnover and have inspired numerous compounds for biomimetic H2 production. Two decades of research on the active site cofactor of [FeFe]-hydrogenases have put forward multiple models of the catalytic proceedings. In comparison, our understanding of proton transfer is poor. Previously, residues were identified forming a hydrogen-bonding network between active site cofactor and bulk solvent; however, the exact mechanism of catalytic proton transfer remained inconclusive. Here, we employ in situ infrared difference spectroscopy on the [FeFe]-hydrogenase from Chlamydomonas reinhardtii evaluating dynamic changes in the hydrogen-bonding network upon photoreduction. While proton transfer appears to be impaired in the oxidized state (Hox), the presented data support continuous proton transfer in the reduced state (Hred). Our analysis allows for a direct, molecular unique assignment to individual amino acid residues. We found that transient protonation changes of glutamic acid residue E141 and, most notably, arginine R148 facilitate bidirectional proton transfer in [FeFe]-hydrogenases. © 2019 American Chemical Society.

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