8E3T

Gallium-reconstituted nitrogenase MoFeP mutant S188A from Azotobacter vinelandii after IDS oxidation

Summary for 8E3T

• Entry DOI: 10.2210/pdb8e3t/pdb
• Descriptor: Nitrogenase molybdenum-iron protein alpha chain, Nitrogenase molybdenum-iron protein beta chain, 3-HYDROXY-3-CARBOXY-ADIPIC ACID, ... (8 entities in total)
• Functional Keywords: mofep, mofe-protein, oxidoreductase
• Biological source: Azotobacter vinelandii DJ; More
• Total number of polymer chains: 4
• Total formula weight: 233141.46

Authors

Rutledge, H.L.,Tezcan, F.A. (deposition date: 2022-08-17, release date: 2022-12-14, Last modification date: 2023-10-25)

Primary citation

Rutledge, H.L.,Field, M.J.,Rittle, J.,Green, M.T.,Tezcan, F.A.
Role of Serine Coordination in the Structural and Functional Protection of the Nitrogenase P-Cluster.
J.Am.Chem.Soc., 144:22101-22112, 2022

PubMed Abstract: Nitrogenase catalyzes the multielectron reduction of dinitrogen to ammonia. Electron transfer in the catalytic protein (MoFeP) proceeds through a unique [8Fe-7S] cluster (P-cluster) to the active site (FeMoco). In the reduced, all-ferrous (P) state, the P-cluster is coordinated by six cysteine residues. Upon two-electron oxidation to the P state, the P-cluster undergoes conformational changes in which a highly conserved oxygen-based residue (a Ser or a Tyr) and a backbone amide additionally ligate the cluster. Previous studies of () MoFeP revealed that when the oxygen-based residue, βSer188, was mutated to a noncoordinating residue, Ala, the P-cluster became redox-labile and reversibly lost two of its eight Fe centers. Surprisingly, the strain with a MoFeP variant that lacked the serine ligand ( βSer188Ala MoFeP) displayed the same diazotrophic growth and enzyme turnover rates as wild-type MoFeP, calling into question the necessity of this conserved ligand for nitrogenase function. Based on these observations, we hypothesized that βSer188 plays a role in protecting the P-cluster under nonideal conditions. Here, we investigated the protective role of βSer188 both and by characterizing the ability of βSer188Ala cells to grow under suboptimal conditions (high oxidative stress or Fe limitation) and by determining the tendency of βSer188Ala MoFeP to be mismetallated . Our results demonstrate that βSer188 (1) increases cell survival upon exposure to oxidative stress in the form of hydrogen peroxide, (2) is necessary for efficient diazotrophic growth under Fe-limiting conditions, and (3) may protect the P-cluster from metal exchange . Taken together, our findings suggest a structural adaptation of nitrogenase to protect the P-cluster via Ser ligation, which is a previously unidentified functional role of the Ser residue in redox proteins and adds to the expanding functional roles of non-Cys ligands to FeS clusters.

PubMed: 36445204
DOI: 10.1021/jacs.2c09480

Experimental method

X-RAY DIFFRACTION (2.2 Å)