Publication Types: Preprint • Symbiosis & Metals

Preprint

Publication Types:

All types ( 63 ) Book Chapter ( 7 ) Comment ( 3 ) Journal Article ( 51 ) Preprint ( 2 )

Medicago truncatula Iron-chaperone 1 (ICHAP1) is required for symbiotic nitrogen fixation

Preprint

Navarro-Gómez C., Collantes-García J.A., Rodríguez-Simón M., Wen J., Castillo-Michel H., Imperial J., Escudero V., González-Guerrero M.

doi: 10.64898/2026.03.29.714480

Publication year: 2026

Abstract

Hundreds of proteins in the cell require iron (Fe) or Fe-containing cofactors to function. However, how Fe²⁺ or Fe³⁺ are specifically allocated to each of these proteins in plant cells remains largely unknown. It has been proposed that Fe metalation could be driven by specific interactions with Fe-shuttling proteins known as Fe-chaperones. Here, we present the first family of plant Fe²⁺-chaperones (ICHAPs) with orthologues in dicots and monocots. The role of these proteins in Fe distribution to Fe-dependent metabolic processes has been illustrated using symbiotic nitrogen fixation in Medicago truncatula root nodules. ICHAP1 is a soluble Fe²⁺-binding protein that interacts with plasma membrane Fe²⁺ transporter NRAMP1, but not with symbiosome Fe²⁺-transporters. ICHAP1 mutants present altered Fe distribution in cells and they cannot fix nitrogen. A second family member, ICHAP2 is required to target Fe²⁺ to symbiosomes, as it accepts Fe²⁺ from ICHAP1 and interacts with symbiosome Fe²⁺-importer VTL8, but not with NRAMP1. These results indicate a path for Fe²⁺ allocation from the plasma membrane to the symbiosome through specific protein-protein interactions and Fe²⁺ exchange from NRAMP1 to ICHAP1, to ICHAP2, and to VTL8.

Competing Interest Statement: The authors have declared no competing interest.

Funder Information Declared

- Ministerio de Ciencia, Innovación y Universidades
- U.S. National Science Foundation, https://ror.org/021nxhr62, DBI-0703285, IOS-1127155, DBI-2233714

Azotobacter vinelandii glutaredoxin D delivers the core [Fe₂S₂] cluster to nitrogenase cofactor scaffold protein NifU

Preprint

García-Collantes J.A., Rosa-Núñez E., Armas A.M., Raimunda D., Pérez-González A., Guo Y., Echávarri-Erasun C., Rubio L.M., González-Guerrero M.

doi: 10.1101/2025.10.21.683637

Publication year: 2025

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.

Keywords: iron; iron-sulfur protein; glutaredoxin; nitrogen fixation; nitrogenase.

Competing Interest Statement: The authors have declared no competing interest.

Funder Information Declared

- Agencia Estatal de Investigación, https://ror.org/003x0zc53, PID2021-12460OB-100, PRE2022-101253, PRE2018-084895, SEV-2016-0672, CEX2020-000999S
- United States Department of Energy, DOE-DE-SC0026054
- Bill and Melinda Gates Foundation, INV-005889
- Gates Foundation, https://ror.org/0456r8d26, INV-067006

The González-Guerrero Lab

Preprint