Characterization of Ferredoxins Involved in Electron Transfer Pathways for Nitrogen Fixation Implicates Differences in Electronic Structure in Tuning 2[4Fe-4S] Fd Activity: Article No. 112521

Nathan Lewis, Effie Kisgeropoulos, Carolyn Lubner, Kathryn Fixen

Research output: Contribution to journalArticlepeer-review

Abstract

Ferredoxins (Fds) are small proteins which shuttle electrons to pathways like biological nitrogen fixation. Physical properties tune the reactivity of Fds with different pathways, but knowledge on how these properties can be manipulated to engineer new electron transfer pathways is lacking. Recently, we showed that an evolved strain of Rhodopseudomonas palustris uses a new electron transfer pathway for nitrogen fixation. This pathway involves a variant of the primary Fd of nitrogen fixation in R. palustris, Fer1, in which threonine at position 11 is substituted for isoleucine (Fer1T11I). To understand why this substitution in Fer1 enables more efficient electron transfer, we used in vivo and in vitro methods to characterize Fer1 and Fer1T11I. Electrochemical characterization revealed both Fer1 and Fer1T11I have similar redox transitions (-480 mV and -550 mV), indicating the reduction potential was unaffected despite the proximity of T11 to an iron-sulfur (Fesingle bondS) cluster of Fer1. Additionally, disruption of hydrogen bonding around an Fesingle bondS cluster in Fer1 by substituting threonine with alanine (T11A) or valine (T11V) did not increase nitrogenase activity, indicating that disruption of hydrogen bonding does not explain the difference in activity observed for Fer1T11I. Electron paramagnetic resonance spectroscopy studies revealed key differences in the electronic structure of Fer1 and Fer1T11I, which indicate changes to the high spin states and/or spin-spin coupling between the Fesingle bondS clusters of Fer1. Our data implicates these electronic structure differences in facilitating electron flow and sets a foundation for further investigations to understand the connection between these properties and intermolecular electron transfer.
Original languageAmerican English
Number of pages12
JournalJournal of Inorganic Biochemistry
Volume254
DOIs
StatePublished - 2024

NREL Publication Number

  • NREL/JA-2700-88385

Keywords

  • electron transfer
  • EPR spectroscopy
  • ferredoxin
  • nitrogen fixation
  • spin coupling

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