7APY image
Entry Detail
PDB ID:
7APY
Keywords:
Title:
Pseudomonas stutzeri nitrous oxide reductase mutant, D576A
Biological Source:
Source Organism:
PDB Version:
Deposition Date:
2020-10-20
Release Date:
2021-01-13
Method Details:
Experimental Method:
Resolution:
1.78 Å
R-Value Free:
0.22
R-Value Work:
0.16
R-Value Observed:
0.16
Space Group:
P 1 21 1
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:Nitrous-oxide reductase
Chain IDs:A, B
Chain Length:646
Number of Molecules:2
Biological Source:Pseudomonas stutzeri
Primary Citation
Histidine-Gated Proton-Coupled Electron Transfer to the Cu A Site of Nitrous Oxide Reductase.
J.Am.Chem.Soc. 143 830 838 (2021)
PMID: 33377777 DOI: 10.1021/jacs.0c10057

Abstact

Copper-containing nitrous oxide reductase (N2OR) is the only known enzyme to catalyze the conversion of the environmentally critical greenhouse gas nitrous oxide (N2O) to dinitrogen (N2) as the final step of bacterial denitrification. Other than its unique tetranuclear active site CuZ, the binuclear electron entry point CuA is also utilized in other enzymes, including cytochrome c oxidase. In the CuA site of Pseudomonas stutzeri N2OR, a histidine ligand was found to undergo a conformational flip upon binding of the substrate N2O between the two copper centers. Here we report on the systematic mutagenesis and spectroscopic and structural characterization of this histidine and surrounding H-bonding residues, based on an established functional expression system for PsN2OR in E. coli. A single hydrogen bond from Ser550 is sufficient to stabilize an unbound conformation of His583, as shown in a Asp576Ala variant, while the additional removal of the hydrogen bond in a Asp576Ala/Ser550Ala double variant compelled His583 to stay in a bound conformation as a ligand to CuA. Systematic mutagenesis of His583 to Ala, Asp, Asn, Glu, Gln, Lys, Phe, Tyr, and Trp showed that although both the CuZ and CuA sites were present in all the variants, only the ones with a protonable side chain, i.e., His, Asp, and Glu, were able to mediate electron transfer at physiological pH. This observation is in line with a proton-coupled electron transfer mechanism at the CuA site of N2OR.

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