
The protonation state of a conserved aspartate residue (Asp64 in Bacillus thermoproteolyticus ferredoxin) acts as a switch, controlling the redox potential and electron transfer in low-potential [4Fe-4S] and [3Fe-4S] ferredoxins.


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Ferredoxin is a small iron-sulfur protein and acts as an electron carrier. Low-potential ferredoxins harbor [4Fe-4S] cluster(s), which play(s) a crucial role as the redox center. Low-potential ferredoxins are able to cover a wide range of redox potentials (−700 to −200 mV); however, the mechanisms underlying the factors which control the redox potential are still enigmatic. Here, we determined the neutron structure of ferredoxin from Bacillus thermoproteolyticus , and experimentally revealed the exact hydrogen-bonding network involving the [4Fe-4S] cluster. The density functional theory calculations based on the hydrogen-bonding network revealed that protonation states of the sidechain of Asp64 close to the [4Fe-4S] cluster critically affected the stability of the reduced state in the cluster. These findings provide the first identification of the intrinsic control factor of redox potential for the [4Fe-4S] cluster in low-potential ferredoxins.

### Competing Interest Statement

The authors have declared no competing interest.

Protonation/deprotonation-driven switch for the redox stability of low-potential [4Fe-4S] ferredoxin

protonation-deprotonation-of-a-conserved-aspartate-residue-determines-the-redox-potential-of-low-potential-ferredoxin


Protonation/Deprotonation of a Conserved Aspartate Residue Determines the Redox Potential of Low-Potential Ferredoxin
