S-methyl-L-cysteine Protects against Antimycin A-induced Mitochondrial Dysfunction in Neural Cells via Mimicking Endogenous Methionine-centered Redox Cycle

Mitochondrial superoxide overproduction is believed to be responsible for the neurotoxicity associated with neurodegeneration.Mitochondria-targeted antioxidants,such as MitoQ,have emerged as potentially effective antioxidant therapies.Methionine sulfoxide reductase A(MsrA)is a key mitochondrial-localized endogenous antioxidative enzyme and it can scavenge oxidizing species by catalyzing the methionine(Met)-centered redox cycle(MCRC).In this study,we observed that the natural L-Met acted as a good scavenger for antimycin A-induced mitochondrial superoxide overproduction in PC12 cells.This antioxidation was largely dependent on the Met oxidase activity of MsrA.S-methyl-L-cysteine(SMLC),a natural analogue of Met that is abundantly found in garlic and cabbage,could activate the Met oxidase activity of MsrA to scavenge free radicals.Furthermore,SMLC protected against antimycin A-induced mitochondrial membrane depolarization and alleviated 1-methyl-4-phenylpyridinium(MPP+)-induced neurotoxicity.Thus,our data highlighted the possibility for SMLC supplement in the detoxication of mitochondrial damage by activating the Met oxidase activity of MsrA.

Protein-Repairing Methionine Sulfoxide Reductases in Photosynthetic Organisms： Gene Organization, Reduction Mechanisms, and Physiological Roles

Methionine oxidation to methionine sulfoxide （MetSO） is reversed by two types of methionine sulfoxide reducrases （MSRs）, A and B, specific to the S- and R-diastereomers of MetSO, respectively. MSR genes are found in most organisms from bacteria to human. In the current review, we first compare the organization of the MSR gene families in photosynthetic organisms from cyanobacteria to higher plants. The analysis reveals that MSRs constitute complex families in higher plants, bryophytes, and algae compared to cyanobacteria and all non-photosynthetic organisms. We also perform a classification, based on gene number and structure, position of redox-active cysteines and predicted sub-cellular localization. The various catalytic mechanisms and potential physiological electron donors involved in the regeneration of MSR activity are then de- scribed. Data available from higher plants reveal that MSRs fulfill an essential physiological function during environmental constraints through a role in protein repair and in protection against oxidative damage. Taking into consideration the ex- pression patterns of MSR genes in plants and the known roles of these genes in non-photosynthetic cells, other functions of MSRs are discussed during specific developmental stages and ageing in photosynthetic organisms.