Azotobacter vinelandii glutaredoxin D delivers the core [Fe 2 S 2 ] cluster to nitrogenase cofactor scaffold protein NifU

2025 · doi:10.1101/2025.10.21.683637
preprint OA: closed
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The study investigates how the nitrogenase cofactor scaffold protein NifU acquires a catalytic [Fe2S2] cluster that is required for assembling the [Fe4S4] precursor clusters used by nitrogenase. Using biochemical assays and mutant analysis in which grxD is altered, the authors find that the glutaredoxin GrxD unidirectionally transfers the [Fe2S2] cluster to NifU via protein-protein interaction, restoring apo-NifU functionality and enabling proper [Fe4S4] synthesis and NifH activation; grxD mutants show reduced nitrogenase activity due to altered iron allocation. The main caveat is that the work focuses on biological nitrogen fixation machinery in vitro/in vivo systems rather than directly examining any disease-relevant iron metabolism pathways. 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

ABSTRACT The scaffold protein NifU plays a central role in assembling the precursor [Fe 4 S 4 ] clusters required for nitrogenase to function. The synthesis of these precursors depends on a catalytic [Fe 2 S 2 ] group within NifU core ferredoxin domain. Here, we show that the monothiol glutaredoxin GrxD delivers this cluster to the NifU scaffold protein. Consistently, grxD mutants have reduced nitrogenase activity, the result of altered iron allocation to this enzyme. Biochemical assays show that GrxD unidirectionally transfers [Fe 2 S 2 ] to NifU through protein-protein interaction. This allows GrxD to restore apo-NifU functionality, enabling proper [Fe 4 S 4 ] synthesis, and NifH activation. These findings are crucial to understand how iron is allocated to nitrogenase for biological nitrogen fixation.
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ABSTRACT The scaffold protein NifU plays a central role in assembling the precursor [Fe4S4] clusters required for nitrogenase to function. The synthesis of these precursors depends on a catalytic [Fe2S2] group within NifU core ferredoxin domain. Here, we show that the monothiol glutaredoxin GrxD delivers this cluster to the NifU scaffold protein. Consistently, grxD mutants have reduced nitrogenase activity, the result of altered iron allocation to this enzyme. Biochemical assays show that GrxD unidirectionally transfers [Fe2S2] to NifU through protein-protein interaction. This allows GrxD to restore apo-NifU functionality, enabling proper [Fe4S4] synthesis, and NifH activation. These findings are crucial to understand how iron is allocated to nitrogenase for biological nitrogen fixation. Competing Interest Statement The authors have declared no competing interest.

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