The role of electrostatic binding interfaces in the performance of bacterial reaction center biophotoelectrodes

Milo R van Moort, Michael R Jones , Raoul N Frese, Vincent M Friebe*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

2 Citations (Scopus)

Abstract

Photosynthetic reaction centers (RCs) efficiently capture and convert solar radiation into electrochemical energy. Accordingly, RCs have the potential as components in biophotovoltaics, biofuel cells, and biosensors. Recent biophotoelectrodes containing the RC from the bacterium Rhodobacter sphaeroides utilize a natural electron donor, horse heart cytochrome c (cyt c), as an electron transfer mediator with the electrode. In this system, electrostatic interfaces largely control the protein-electrode and protein-protein interactions necessary for electron transfer. However, recent studies have revealed kinetic bottlenecks in cyt-mediated electron transfer that limit biohybrid photoelectrode efficiency. Here, we seek to understand how changing protein-protein and protein-electrode interactions influence RC turnover and biophotoelectrode efficiency. The RC-cyt c binding interaction was modified by substituting interfacial RC amino acids. Substitutions Asn-M188 to Asp and Gln-L264 to Glu, which are known to produce a higher cyt-binding affinity, led to a decrease in RC turnover frequency (TOF) at the electrode, suggesting a decrease in cyt c dissociation was rate-limiting in these RC variants. Conversely, an Asp-M88 to Lys substitution producing a lower binding affinity had little effect on RC TOF, suggesting a decrease in cyt c association rate was not a rate-limiting factor. Modulating the electrode surface with a self-assembled monolayer that oriented the cyt c to face the electrode did not affect RC TOF, suggesting that the orientation of cyt c was also not a rate-limiting factor. Changing the ionic strength of the electrolyte solution had the most potent impact on RC TOF, indicating that cyt c mobility was important for effective electron donation to the photo-oxidized RC. An ultimate limitation for RC TOF was that cyt c desorbed from the electrode at ionic strengths above 120 mM, diluting its local concentration near the electrode-adsorbed RCs, and resulting in poor biophotoelectrode performance. These findings will guide further tuning of these interfaces for improved performance.
Original languageEnglish
Pages (from-to)3044–3051
Number of pages8
JournalACS Sustainable Chemistry and Engineering
Volume11
Issue number7
DOIs
Publication statusPublished - 7 Feb 2023

Bibliographical note

Funding Information:
V.M.F. acknowledges support from the Dutch Research Council NWO for a Veni grant project no. 16866 and the Marie Skłodowska-Curie grant agreement no. 101068908. R.N.F. acknowledges support from the Dutch Research Council NWO for a Vidi grant project no. 14595. Molecular graphics were performed with UCSF ChimeraX, developed by the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco, with support from National Institutes of Health R01-GM129325 and the Office of Cyber Infrastructure and Computational Biology, National Institute of Allergy and Infectious Diseases.

Publisher Copyright:
© 2023 The Authors. Published by American Chemical Society.

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