Studies On The Physiological Function And Antioxidative Mechanisms Of Methionine Sulfoxide Reductase In Corynebacterium Glutamicum

Methionine is an essential amino acid,which is necessary for the methylation and vulcanization of proteins.And it has important biochemical functions for maintaining normal biological life.However,Methionine is very sensitive to be oxidized into methionine sulfoxide(Met O)which contains two classes,methionine-S-sulfoxide(Met-S-O)and methionine-R-sulfoxide(Met-R-O).Oxidation of the key parts in proteins will lead to changes in protein conformation and causing loss of biological activities.If there is no repairing mechanism,it could be fatal injuries for bodies.Methionine sulphoxide reductases(Msr)present in most living organisms are antioxidant repair enzymes that catalyze the reduction of Met O to Met in free and protein-bound forms,which contain two unrelated classes,methionine sulphoxide reductase A(Msr A)and methionine sulphoxide reductase B(Msr B).Msr A is very specific for reduction of the S-isomer of Met O and the other,Msr B,is specific for reduction of the R-isomer of Met O.In this study,we used Corynebacterium glutamicum as the research object to study the physiological function of Msr B,explore the antioxidant mechanism of Msr B and compare its similarities and differences with Msr A.The results are as follows:1.By multi-sequence alignment analysis,the sequence of the protein which is encoded by ncgl1823 is closely related to the Msr B protein sequence in Mycobacterium tuberculosis and Escherichia coli.Through the analysis of active sites,it was confirmed that ncgl1823 is the gene encoding Msr B in Corynebacterium glutamicum.2.By comparing the reduction ability of Met O and the kinetic experiments,we concluded that Msr B has a certain ability to reduce Met O to Met,however,the ability of Msr A is greater than Msr B.3.By comparing the survival rates to different oxidative stresses,it was found that Msr B plays a limited effect on the process of antioxidant stress in this bacteria,while Msr A plays a major role.4.By the experiments of the formation and separation of heterodimers and the kinetic experiments,it was found that Msr B uses thioredoxin/thioredoxin reductase(Trx/Trx R)reducing system as electron donors but independent from the mycoredoxin 1/mycothione reductase/mycothiol(Mrx1/Mtr/MSH)system to relalize the reducing of Met O and the regeneration.5.Sig H can not only regulate the expression of msr A but also regulate the expression of msr B;but the expression of msr B is not induced by oxidative stress.