How [FeFe]-Hydrogenase Facilitates Bidirectional Proton Transfer

Area of Science:

• Biochemistry
• Bioenergetics
• Enzymology

Background:

• Hydrogenases are metalloenzymes catalyzing interconversion of molecular hydrogen (H₂) and protons.
• [FeFe]-hydrogenases are known for high H₂ turnover rates, inspiring biomimetic H₂ production.
• Proton transfer mechanisms in [FeFe]-hydrogenases remain poorly understood despite extensive research on their active site.

Purpose of the Study:

• To elucidate the mechanism of catalytic proton transfer in [FeFe]-hydrogenases.
• To investigate dynamic changes in the hydrogen-bonding network during photoreduction.
• To identify specific amino acid residues involved in proton transfer.

Main Methods:

• In situ infrared difference spectroscopy was used.
• The [FeFe]-hydrogenase from *Chlamydomonas reinhardtii* was studied.
• Dynamic changes in the hydrogen-bonding network upon photoreduction were evaluated.

Main Results:

• Proton transfer appears impaired in the oxidized state (H_ox) but continuous in the reduced state (H_red).
• Transient protonation changes of glutamic acid (E141) and arginine (R148) were identified.
• Bidirectional proton transfer is facilitated by these specific residues.

Conclusions:

• Continuous proton transfer occurs in the reduced state of [FeFe]-hydrogenases.
• Arginine R148 and glutamic acid E141 play crucial roles in facilitating proton transfer.
• This study provides molecular insights into proton relay mechanisms in hydrogenases.