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ABSTRACT Nitrogenase iron (Fe) proteins reduce CO 2 to CO and/or hydrocarbons under ambient conditions. Here, we report a 2.4-Å crystal structure of the Fe protein from Methanosarcina acetivorans ( Ma NifH), which is generated in the presence of a reductant, dithionite, and an alternative CO 2 source, bicarbonate. Structural analysis of this methanogen Fe protein species suggests that CO 2 is possibly captured in an unactivated, linear conformation near the [Fe 4 S 4 ] cluster of Ma NifH by a conserved arginine (Arg) pair in a concerted and, possibly, asymmetric manner. Density functional theory calculations and mutational analyses provide further support for the capture of CO 2 on Ma NifH while suggesting a possible role of Arg in the initial coordination of CO 2 via hydrogen bonding and electrostatic interactions. These results provide a useful framework for further mechanistic investigations of CO 2 activation by a surface-exposed [Fe 4 S 4 ] cluster, which may facilitate future development of FeS catalysts for ambient conversion of CO 2 into valuable chemical commodities. IMPORTANCE This work reports the crystal structure of a previously uncharacterized Fe protein from a methanogenic organism, which provides important insights into the structural properties of the less-characterized, yet highly interesting archaeal nitrogenase enzymes. Moreover, the structure-derived implications for CO 2 capture by a surface-exposed [Fe 4 S 4 ] cluster point to the possibility of developing novel strategies for CO 2 sequestration while providing the initial insights into the unique mechanism of FeS-based CO 2 activation.
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Characterization of a Nitrogenase Iron Protein Substituted with a Synthetic [Fe 4 Se 4 ] Cluster
Abstract The Fe protein of nitrogenase plays multiple roles in substrate reduction and cluster maturation via its redox‐active [Fe4S4] cluster. Here we report the synthesis and characterization of a water‐soluble [Fe4Se4] cluster that is used to substitute the [Fe4S4] cluster of theAzotobacter vinelandiiFe protein (AvNifH). Biochemical, EPR and XAS/EXAFS analyses demonstrate the ability of the [Fe4Se4] cluster to adopt the super‐reduced, all‐ferrous state upon its incorporation intoAvNifH. Moreover, these studies reveal that the [Fe4Se4] cluster inAvNifH already assumes a partial all‐ferrous state ([Fe4Se4]0) in the presence of dithionite, where its [Fe4S4] counterpart inAvNifH exists solely in the reduced state ([Fe4S4]1+). Such a discrepancy in the redox properties of theAvNifH‐associated [Fe4Se4] and [Fe4S4] clusters can be used to distinguish the differential redox requirements for the substrate reduction and cluster maturation of nitrogenase, pointing to the utility of chalcogen‐substituted FeS clusters in future mechanistic studies of nitrogenase catalysis and assembly.
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- Award ID(s):
- 1651398
- PAR ID:
- 10368319
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 61
- Issue:
- 19
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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