MSRA

MSRA Full Name

methionine sulfoxide reductase A

MSRA Introduction

Methionine sulfoxide reductase A (MSRA) is a stereospecific oxidoreductase that catalyzes the thioredoxin-dependent reduction of methionine-S-sulfoxide (Met-S-SO) back to methionine. Encoded by the MSRA gene on chromosome 8p23.1, MSRA belongs to the methionine sulfoxide reductase (Msr) family of antioxidant repair enzymes that function to reverse oxidative damage to proteins. Methionine residues in proteins are susceptible to oxidation by reactive oxygen species (ROS) and reactive nitrogen species (RNS), generating methionine sulfoxide diastereomers — MSRA specifically reduces the S-epimer, while MSRB enzymes reduce the R-epimer. Together, these enzymes constitute a critical protein repair system that maintains cellular proteome integrity under oxidative stress.

Figure 1. Strcuture of methionine sulfoxide reductase A.

Catalytic Mechanism of Methionine Sulfoxide Repair
MSRA employs a unique catalytic mechanism involving a conserved cysteine residue (Cys72 in the human enzyme) that acts as a nucleophile to attack the sulfur atom of methionine-S-sulfoxide, forming a sulfenic acid intermediate and releasing repaired methionine. The catalytic cysteine is then regenerated through a thiol-disulfide exchange cascade involving a resolving cysteine (Cys218) and the thioredoxin/thioredoxin reductase system, which provides the reducing equivalents from NADPH. The enzyme adopts a conserved α/β fold and binds its substrate in a stereospecific pocket that discriminates between the S- and R-epimers of methionine sulfoxide. MSRA also reduces free methionine sulfoxide, contributing to the recycling of this amino acid for new protein synthesis. MSRA expression and activity are regulated by oxidative stress-responsive transcription factors including FoxO and Nrf2, linking its function to the broader cellular antioxidant defense network.

MSRA in Oxidative Stress, Aging, and Neurodegenerative Disease
MSRA has been implicated as an important determinant of longevity and healthy aging across species: overexpression of MsrA extends lifespan in Drosophila melanogaster, while MsrA knockout mice exhibit shortened lifespan, increased protein carbonyl content, and neurological dysfunction, suggesting a causal relationship between methionine oxidation repair and organismal aging. In the brain, MSRA is highly expressed in neurons, particularly in the cerebellum and hippocampus, and reduced MSRA activity has been observed in postmortem brain tissue from Alzheimer's disease patients, where accumulated methionine-oxidized proteins including oxidized amyloid-β peptide may contribute to neurotoxicity. MSRA dysfunction has also been linked to Parkinson's disease and age-related macular degeneration, the latter through impaired repair of oxidized methionine residues in retinal pigment epithelial cells. Pharmacological activation of MSRA or supplementation with methionine sulfoxide scavengers represents a potential therapeutic strategy for oxidative stress-related pathologies.

Alternate Names for MSRA

MSRA; methionine sulfoxide reductase A; PMSR; mitochondrial peptide methionine sulfoxide reductase; peptide Met(O) reductase; peptide met (O) reductase; peptide-methionine (S)-S-oxide reductase; cytosolic methionine-S-sulfoxide reductase;