A Single Active-Site Water Molecule Encodes Two Distinct Proton-Coupled Electron Transfer Pathways in Fatty Acid Photodecarboxylase
- 1University of L’aquila , , via Vetoio (Coppito 1) , ,
- 2Shanghai Jiao Tong University , , ,
Abstract
Water molecules are key actors in enzymatic proton-coupled electron transfer (PCET), yet their mechanistic versatility remains underexplored. Using a multiscale computational approach, we show that a previously unidentified water molecule (Wat3) in fatty acid photodecarboxylase (FAP), a natural photoenzyme converting fatty acids into alkanes, mediates radical quenching via two PCET pathways: in the dominant one, which qualitatively agrees with the 100 ns experimental time scale, Wat3 stabilizes the transition state for direct proton transfer from Cys432 to the alkyl radical; in the alternative, the same molecule acts as a proton shuttle in a quasi-concerted two-proton transfer, with the flavin semiquinone providing the electron in both cases. The minor pathway, though less accessible in wild-type FAP, may become operative in engineered variants or related enzymes. Additionally, CO2 reacts with the thiolate to yield a thiocarbonate adduct, explaining unassigned crystallographic electron density. These results show how a single water molecule encodes mechanistic diversity in enzymatic PCET.
Versions
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BibTeX
@article{dellorletta2026single,
title = {{A Single Active-Site Water Molecule Encodes Two Distinct Proton-Coupled Electron Transfer Pathways in Fatty Acid Photodecarboxylase}},
author = {Gianluca Dell’Orletta and Dongping Zhong and Massimiliano Aschi and Isabella Daidone},
journal = {ACS Omega},
year = {2026},
month = oct,
doi = {10.1021/acsomega.6c06141},
url = {https://pubs.acs.org/acsodf/article/doi/10.1021/acsomega.6c06141/5455830/A-Single-Active-Site-Water-Molecule-Encodes-Two},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - A Single Active-Site Water Molecule Encodes Two Distinct Proton-Coupled Electron Transfer Pathways in Fatty Acid Photodecarboxylase
AU - Gianluca Dell’Orletta
AU - Dongping Zhong
AU - Massimiliano Aschi
AU - Isabella Daidone
PY - 2026
DA - 2026/10/21
JO - ACS Omega
DO - 10.1021/acsomega.6c06141
UR - https://pubs.acs.org/acsodf/article/doi/10.1021/acsomega.6c06141/5455830/A-Single-Active-Site-Water-Molecule-Encodes-Two
AB - Water molecules are key actors in enzymatic proton-coupled electron transfer (PCET), yet their mechanistic versatility remains underexplored. Using a multiscale computational approach, we show that a previously unidentified water molecule (Wat3) in fatty acid photodecarboxylase (FAP), a natural photoenzyme converting fatty acids into alkanes, mediates radical quenching via two PCET pathways: in the dominant one, which qualitatively agrees with the 100 ns experimental time scale, Wat3 stabilizes the transition state for direct proton transfer from Cys432 to the alkyl radical; in the alternative, the same molecule acts as a proton shuttle in a quasi-concerted two-proton transfer, with the flavin semiquinone providing the electron in both cases. The minor pathway, though less accessible in wild-type FAP, may become operative in engineered variants or related enzymes. Additionally, CO2 reacts with the thiolate to yield a thiocarbonate adduct, explaining unassigned crystallographic electron density. These results show how a single water molecule encodes mechanistic diversity in enzymatic PCET.
SN - 2470-1343
ER -