Accéder directement au contenu Accéder directement à la navigation
Article dans une revue

Structural insights into the mechanism of the radical SAM carbide synthase NifB, a key nitrogenase cofactor maturating enzyme

Abstract : Nitrogenase is a key player in the global nitrogen cycle as it catalyzes the reduction of dinitrogen into ammonia. The active site of the nitrogenase MoFe protein corresponds to a [MoFe7S9C-(R)-homocitrate] species designated FeMo-cofactor, whose biosynthesis and insertion requires the action of over a dozen maturation proteins provided by the NIF (for NItrogen Fixation) assembly machinery. Among them, the radical SAM protein NifB plays an essential role, concomitantly inserting a carbide ion and coupling two [Fe4S4] clusters to form a [Fe8S9C] precursor called NifB-co. Here we report on the X-ray structure of NifB from Methanotrix thermoacetophila at 1.95 Å resolution in a state pending the binding of one [Fe4S4] cluster substrate. The overall NifB architecture indicates that this enzyme has a single SAM binding site, which at this stage is occupied by cysteine residue 62. The structure reveals a unique ligand binding mode for the K1 cluster involving cysteine residues 29 and 128 in addition to histidine 42 and glutamate 65. The latter, together with cysteine 62, belongs to a loop inserted in the active site, likely protecting the already present [Fe4S4] clusters. These two residues regulate the sequence of events, controlling SAM dual reactivity and preventing unwanted radical-based chemistry before the K2 [Fe4S4] cluster substrate is loaded into the protein. The location of K1 cluster, too far away from the SAM binding site, supports a mechanism in which the K2 cluster is the site of methylation.
Type de document :
Article dans une revue
Liste complète des métadonnées

https://hal.univ-grenoble-alpes.fr/hal-02775951
Contributeur : Frank Thomas <>
Soumis le : jeudi 4 juin 2020 - 14:53:24
Dernière modification le : mercredi 26 août 2020 - 16:58:02

Identifiants

Collections

Citation

Ana Sosa Fajardo, Pierre Legrand, Lucía Payá-Tormo, Lydie Martin, Maria Teresa Pellicer Martinez, et al.. Structural insights into the mechanism of the radical SAM carbide synthase NifB, a key nitrogenase cofactor maturating enzyme. Journal of the American Chemical Society, American Chemical Society, 2020, ⟨10.1021/jacs.0c02243⟩. ⟨hal-02775951⟩

Partager

Métriques

Consultations de la notice

40