An unexpected P-cluster like intermediate en route to the nitrogenase FeMo-co. Issue 14 (8th March 2021)

• Record Type: Journal Article
• Authors: Jenner, Leon P.; Cherrier, Mickael V.; Amara, Patricia; Rubio, Luis M.; Nicolet, Yvain
• Is Part Of: Chemical science. Volume 12:Issue 14(2021)
• Page Start: 5269
• Page End: 5274
• Publication Date: 2021-03-08
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc00289a
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : The K-cluster of NifB as a key intermediate in the synthesis of the nitrogenase active site supports [Fe4 S4 ] cluster fusion occurs before carbide and sulfide insertion and displays ligand spatial arrangement reminiscent to that of the P-cluster. Abstract : The nitrogenase MoFe protein contains two different FeS centers, the P-cluster and the iron–molybdenum cofactor (FeMo-co). The former is a [Fe8 S7 ] center responsible for conveying electrons to the latter, a [MoFe7 S9 C-( R )-homocitrate] species, where N2 reduction takes place. NifB is arguably the key enzyme in FeMo-co assembly as it catalyzes the fusion of two [Fe4 S4 ] clusters and the insertion of carbide and sulfide ions to build NifB-co, a [Fe8 S9 C] precursor to FeMo-co. Recently, two crystal structures of NifB proteins were reported, one containing two out of three [Fe4 S4 ] clusters coordinated by the protein which is likely to correspond to an early stage of the reaction mechanism. The other one was fully complemented with the three [Fe4 S4 ] clusters (RS, K1 and K2), but was obtained at lower resolution and a satisfactory model was not obtained. Here we report improved processing of this crystallographic data. At odds with what was previously reported, this structure contains a unique [Fe8 S8 ] cluster, likely to be a NifB-co precursor resulting from the fusion of K1- and K2-clusters. Strikingly, this new [Fe8 S8 ] cluster has both a structure and coordination sphere geometry reminiscent of the fully reduced P-cluster (P N -state) with an additional μ 2 -bridging sulfide ion pointing toward the RS cluster. Comparison of available NifB structures further unveils the plasticity of this protein and suggests how ligand reorganization would accommodate cluster loading and fusion in the time-course of NifB-co synthesis.