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

2024 · doi:10.1101/2024.09.12.612615
preprint OA: closed CC-BY-4.0
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The paper investigates how low-potential [4Fe-4S] ferredoxins maintain redox stability across a broad redox potential range, focusing on the structural and electronic determinants controlling the reduced cluster state. Using neutron crystal structure determination of ferredoxin from Bacillus thermoproteolyticus, the authors experimentally mapped the hydrogen-bonding network around the [4Fe-4S] cluster and applied density functional theory to model how this network affects protonation-dependent energetics. They found that protonation states of the side chain of Asp64 near the cluster critically influence the stability of the reduced [4Fe-4S] state, identifying an intrinsic control factor for redox potential. The limitation is that the mechanistic conclusion is grounded in a specific ferredoxin structure and the associated computational modeling, rather than demonstrating generality across all low-potential ferredoxins. The paper does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.

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Abstract

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.
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Abstract 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. Footnotes Supplementary Figure 9S and its legend have been moved into the main text as Figure 6.

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