6CZ8

The arsenate respiratory reductase (Arr) complex from Shewanella sp. ANA-3 bound to arsenate

Summary for 6CZ8

• Entry DOI: 10.2210/pdb6cz8/pdb
• Descriptor: ArrA, 4Fe-4S ferredoxin, iron-sulfur binding domain protein, IRON/SULFUR CLUSTER, ... (10 entities in total)
• Functional Keywords: arsenate, molybdoprotein, molybdopterin, oxidoreductase
• Biological source: Shewanella sp. (strain ANA-3); More
• Total number of polymer chains: 4
• Total formula weight: 241549.29

Authors

Glasser, N.R.,Newman, D.K. (deposition date: 2018-04-08, release date: 2018-08-15, Last modification date: 2024-03-13)

Primary citation

Glasser, N.R.,Oyala, P.H.,Osborne, T.H.,Santini, J.M.,Newman, D.K.
Structural and mechanistic analysis of the arsenate respiratory reductase provides insight into environmental arsenic transformations.
Proc. Natl. Acad. Sci. U.S.A., 115:E8614-E8623, 2018

PubMed Abstract: Arsenate respiration by bacteria was discovered over two decades ago and is catalyzed by diverse organisms using the well-conserved Arr enzyme complex. Until now, the mechanisms underpinning this metabolism have been relatively opaque. Here, we report the structure of an Arr complex (solved by X-ray crystallography to 1.6-Å resolution), which was enabled by an improved Arr expression method in the genetically tractable arsenate respirer sp. ANA-3. We also obtained structures bound with the substrate arsenate (1.8 Å), the product arsenite (1.8 Å), and the natural inhibitor phosphate (1.7 Å). The structures reveal a conserved active-site motif that distinguishes Arr [(R/K)GRY] from the closely related arsenite respiratory oxidase (Arx) complex (XGRGWG). Arr activity assays using methyl viologen as the electron donor and arsenate as the electron acceptor display two-site ping-pong kinetics. A Mo(V) species was detected with EPR spectroscopy, which is typical for proteins with a pyranopterin guanine dinucleotide cofactor. Arr is an extraordinarily fast enzyme that approaches the diffusion limit ( = 44.6 ± 1.6 μM, = 9,810 ± 220 seconds), and phosphate is a competitive inhibitor of arsenate reduction ( = 325 ± 12 μM). These observations, combined with knowledge of typical sedimentary arsenate and phosphate concentrations and known rates of arsenate desorption from minerals in the presence of phosphate, suggest that () arsenate desorption limits microbiologically induced arsenate reductive mobilization and () phosphate enhances arsenic mobility by stimulating arsenate desorption rather than by inhibiting it at the enzymatic level.

PubMed: 30104376
DOI: 10.1073/pnas.1807984115

Experimental method

X-RAY DIFFRACTION (1.78 Å)