The Crystal Structure of Plant Sulfite Oxidase Provides Insights into Sulfite Oxidation in Plants and Animals

Abstract

The molybdenum cofactor (Moco) containing sulfite oxidase (SO) from Arabidopsis thaliana has recently been identified and biochemically characterized. The enzyme is found in peroxisomes and believed to detoxify excess sulfite that is produced during sulfur assimilation, or due to air pollution. Plant SO (PSO) is homodimeric and homologous to animal SO, but contains only a single Moco domain without an additional redox center. Here, we present the first crystal structure of a plant Moco enzyme, the apo-state of Arabidopsis SO at 2.6 A resolution. The overall fold and coordination of the Moco are similar to chicken SO (CSO). Comparisons of conserved surface residues and the charge distribution in PSO and CSO reveal major differences near the entrance to both active sites reflecting different electron acceptors. Arg374 has been identified as an important substrate binding residue due to its conformational change when compared to the sulfate bound structure of CSO.

Direct Demonstration of the Presence of Coordinated Sulfate in the Reaction Pathway of Arabidopsis thaliana Sulfite Oxidase Using 33S Labeling and ESEEM Spectroscopy

“…The fact that this line dominates the spectra and shows very little orientational dependence leads to the suggestion that it corresponds to the electron spin manifold where the 33 S Zeeman interaction is approximately cancelled by the hfi (ν I − A/2 ~ 0). Therefore, this frequency should be close to ΔE Q (see eq 4), and the quadrupole coupling constant can immediately be estimated as e 2 Qq/h ~ 36 MHz.…”

“…The quadrupolar spin-Hamiltonian is: (1) where k for I = 3/2 is equal to e 2 Qq/12h and η is the asymmetry parameter of the electric field gradient tensor on the nucleus: 0 ≤ η ≤ 1. The energies and eigenfunctions of H Q are: (2) where c α = cosα, s α = sinα, and . Note that the largest value of α is only 15° (reached for η = 1), and therefore s α < 0.26.…”

Design, synthesis, and characterization of a sterically encumbered dioxo molybdenum (VI) core

“…Yield = 82% (4.44 g). 1 Synthesis of 4. To a solution of 3 (2.87 g, 3.04 mmol) in THF (40 mL) and DMF (0.2 mL) oxalyl chloride (11.6 mL, 91.2 mmol) at 0°C was slowly added and the resulting light yellow solution was gradually warmed to room temperature and stirred for 6 h. Evaporation of the solvent under reduced pressure yielded a yellow solid, which was redissolved in CH 2 Cl 2 .…”

“…Yield = 72% (7.24 g). 1 Synthesis of 5. At 0°C to a solution of 4(1.17 g, 0.48 mmol) in EtOH and THF (10mL/ 10mL) NaBH 4 (75 mg, 1.92 mmol) was added and the reaction mixture was stirred for additional 4h.…”

“…The formation of the dinuclear compounds in these systems underscores the pervasive nature of the dinucleation reaction especially with smaller ligand architectures. (1) In this paper we offer a different approach where we have used larger dendritic ligand system to prevent the dinucleation. In general, the dendritic ligand architectures provide an opportunity to accomplish encapsulation on the molecular scale.…”