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Addressing Serine Lability in a Paramagnetic Dimethyl Sulfoxide Reductase Catalytic Intermediate.

ABSTRACT: Two new desoxo molybdenum(V) complexes have been synthesized and characterized as models for the paramagnetic high-g split intermediate observed in the catalytic cycle of dimethyl sulfoxide reductase (DMSOR). Extended X-ray absorption fine structure (EXAFS) and electron paramagnetic resonance (EPR) data are used to provide new insight into the geometric and electronic structures of high-g split and other EPR-active type II/III DMSOR family enzyme forms. The results support a 6-coordinate [(PDT)₂Mo(OH)(O_Ser)]^- structure (PDT = pyranopterin dithiolene) for a high-g split with four S donors from two PDT ligands, a coordinated hydroxyl ligand, and a serinate O donor. This geometry orients the redox orbital toward the substrate access channel for the two-electron reduction of substrates.

SUBMITTER: Kc K

PROVIDER: S-EPMC9070986 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Spectroscopic and electronic structure studies of a dimethyl sulfoxide reductase catalytic intermediate: implications for electron- and atom-transfer reactivity.

Project description:The electronic structure of a genuine paramagnetic des-oxo Mo(V) catalytic intermediate in the reaction of dimethyl sulfoxide reductase (DMSOR) with (CH(3))(3)NO has been probed by electron paramagnetic resonance (EPR), electronic absorption, and magnetic circular dichroism (MCD) spectroscopies. EPR spectroscopy reveals rhombic g- and A-tensors that indicate a low-symmetry geometry for this intermediate and a singly occupied molecular orbital that is dominantly metal centered. The excited-state spectroscopic data were interpreted in the context of electronic structure calculations, and this has resulted in a full assignment of the observed MCD and electronic absorption bands, a detailed understanding of the metal-ligand bonding scheme, and an evaluation of the Mo(V) coordination geometry and Mo(V)-S(dithiolene) covalency as it pertains to the stability of the intermediate and electron-transfer regeneration. Finally, the relationship between des-oxo Mo(V) and des-oxo Mo(IV) geometric and electronic structures is discussed relative to the reaction coordinate in members of the DMSOR enzyme family.

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Reduction of Protein Bound Methionine Sulfoxide by a Periplasmic Dimethyl Sulfoxide Reductase.

Project description:In proteins, methionine (Met) can be oxidized into Met sulfoxide (MetO). The ubiquitous methionine sulfoxide reductases (Msr) A and B are thiol-oxidoreductases reducing MetO. Reversible Met oxidation has a wide range of consequences, from protection against oxidative stress to fine-tuned regulation of protein functions. Bacteria distinguish themselves by the production of molybdenum-containing enzymes reducing MetO, such as the periplasmic MsrP which protects proteins during acute oxidative stress. The versatile dimethyl sulfoxide (DMSO) reductases were shown to reduce the free amino acid MetO, but their ability to reduce MetO within proteins was never evaluated. Here, using model oxidized proteins and peptides, enzymatic and mass spectrometry approaches, we showed that the Rhodobacter sphaeroides periplasmic DorA-type DMSO reductase reduces protein bound MetO as efficiently as the free amino acid L-MetO and with catalytic values in the range of those described for the canonical Msrs. The identification of this fourth type of enzyme able to reduce MetO in proteins, conserved across proteobacteria and actinobacteria, suggests that organisms employ enzymatic systems yet undiscovered to regulate protein oxidation states.

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Addressing Ligand-Based Redox in Molybdenum-Dependent Methionine Sulfoxide Reductase.

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Dimethyl sulfide protects against oxidative stress and extends lifespan via a methionine sulfoxide reductase A-dependent catalytic mechanism.

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| S-EPMC308893 | biostudies-literature

Interaction of product analogues with the active site of rhodobacter sphaeroides dimethyl sulfoxide reductase.

Project description:We report a structural characterization using X-ray absorption spectroscopy of Rhodobacter sphaeroides dimethyl sulfoxide (DMSO) reductase reduced with trimethylarsine and show that this is structurally analogous to the physiologically relevant dimethyl sulfide reduced DMSO reductase. Our data unambiguously indicate that these species should be regarded as formal MoIV species and indicate a classical coordination complex of trimethylarsine oxide, with no special structural distortions. The similarity of the trimethylarsine and dimethyl sulfide complexes suggests, in turn, that the dimethyl sulfide reduced enzyme possesses a classical coordination of DMSO with no special elongation of the S-O bond, as previously suggested.

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cis-Dichlorido-tetra-kis-(dimethyl sulfoxide-?O)chromium(III) chloride dimethyl sulfoxide monosolvate.

Project description:The structure of the title compound, [CrCl2(C2H6OS)4]Cl·C2H6OS, consists of a Cr(III) ion coordinated by four O atoms of dimethyl sulfoxide (DMSO) ligands and two chloride ions in cis positions, forming a distorted CrCl2O4 octa-hedron. An isolated Cl(-) counter-anion and a positionally disordered DMSO mol-ecule [occupancy ratio 0.654?(4):0.346?(4)] are also present. In the structure, the complex cations inter-act with the Cl(-) counter-anions and the DMSO solvent mol-ecules via weak C-H?Cl and C-H?O inter-actions, forming a three-dimensional network.

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(Dimethyl sulfoxide-?O)bis-(thio-semicarbazide-?N,S)zinc dipicrate dimethyl sulfoxide solvate monohydrate.

Project description:The title complex, [Zn(CH(5)N(3)S)(2)(C(2)H(6)OS)](C(6)H(2)N(3)O(7))(2)·C(2)H(6)OS·H(2)O, is composed of a [Zn(thio-semi-carbazide)(2)(DMSO)](2+) cation (where DMSO is dimethyl sulfoxide), and two picrate anions. In the asymmetric unit, there is also a solvent mol-ecule of DMSO and a water mol-ecule of crystallization. In the cation, the Zn(II) atom is five-coordinated in a distorted square-pyramidal geometry. It coordinates to the O atom of a DMSO mol-ecule and to the S and one N atom of two thio-semicarbazide mol-ecules, which behave as bidentate ligands coordinating in a trans arrangement. In the crystal, a number of N-H?O, O-H?O and N-H?S hydrogen bonds link the mol-ecules into two-dimensional networks. These networks are further linked via weak C-H?O inter-actions, forming a three-dimensional arrangement. Positional disorder in one methyl group of the coordinated DMSO molecule and in the two picrate anions was observed.

| S-EPMC3051735 | biostudies-literature

Increased catalytic efficiency following gene fusion of bifunctional methionine sulfoxide reductase enzymes from Shewanella oneidensis.

Project description:Methionine sulfoxide reductase enzymes MsrA and MsrB have complementary stereospecificities that reduce the S and R stereoisomers of methionine sulfoxide (MetSO), respectively, and together function as critical antioxidant enzymes. In some pathogenic and metal-reducing bacteria, these genes are fused to form a bifunctional methionine sulfoxide reductase (i.e., MsrBA) enzyme. To investigate how gene fusion affects the substrate specificity and catalytic activities of Msr, we have cloned and expressed the MsrBA enzyme from Shewanella oneidensis, a metal-reducing bacterium and fish pathogen. For comparison, we also cloned and expressed the wild-type MsrA enzyme from S. oneidensis and a genetically engineered MsrB protein. MsrBA is able to completely reduce (i.e., repair) MetSO in the calcium regulatory protein calmodulin (CaM), while only partial repair is observed using both MsrA and MsrB enzymes together at 25 degrees C. A restoration of the normal protein fold is observed co-incident with the repair of MetSO in oxidized CaM (CaMox by MsrBA, as monitored by time-dependent increases in the anisotropy associated with the rigidly bound multiuse affinity probe 4',5'-bis(1,3,2-dithioarsolan-2-yl)fluorescein (FlAsH). Underlying the efficient repair of MetSO in CaMox is the coordinate activity of the two catalytic domains in the MsrBA fusion protein, which results in a 1 order of magnitude rate enhancement in comparison to those of the individual MsrA or MsrB enzyme alone. The coordinate binding of both domains of MsrBA permits the full repair of all MetSO in CaMox. The common expression of Msr fusion proteins in bacterial pathogens is consistent with an important role for this enzyme activity in the maintenance of protein function necessary for bacterial survival under highly oxidizing conditions associated with pathogenesis or bioremediation.

| S-EPMC2546871 | biostudies-literature

Thiol-disulfide exchange is involved in the catalytic mechanism of peptide methionine sulfoxide reductase.

Project description:Peptide methionine sulfoxide reductase (MsrA; EC ) reverses the inactivation of many proteins due to the oxidation of critical methionine residues by reducing methionine sulfoxide, Met(O), to methionine. MsrA activity is independent of bound metal and cofactors but does require reducing equivalents from either DTT or a thioredoxin-regenerating system. In an effort to understand these observations, the four cysteine residues of bovine MsrA were mutated to serine in a series of permutations. An analysis of the enzymatic activity of the variants and their free sulfhydryl states by mass spectrometry revealed that thiol-disulfide exchange occurs during catalysis. In particular, the strictly conserved Cys-72 was found to be essential for activity and could form disulfide bonds, only upon incubation with substrate, with either Cys-218 or Cys-227, located at the C terminus. The significantly decreased activity of the Cys-218 and Cys-227 variants in the presence of thioredoxin suggested that these residues shuttle reducing equivalents from thioredoxin to the active site. A reaction mechanism based on the known reactivities of thiols with sulfoxides and the available data for MsrA was formulated. In this scheme, Cys-72 acts as a nucleophile and attacks the sulfur atom of the sulfoxide moiety, leading to the formation of a covalent, tetracoordinate intermediate. Collapse of the intermediate is facilitated by proton transfer and the concomitant attack of Cys-218 on Cys-72, leading to the formation of a disulfide bond. The active site is returned to the reduced state for another round of catalysis by a series of thiol-disulfide exchange reactions via Cys-227, DTT, or thioredoxin.

| S-EPMC18625 | biostudies-other

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