Abstract:

The mutant strain of Saccharomyces cerevisiae Y518 yielded much more glutathione than the starting strain and presented an excellent acid resistance. The changes in glutathione synthase sequence and structure before and after mutation were analyzed using bioinformatics tools to account for the reason why the acid resistance was increased. The rigid residue Pro was replaced by flexible residue Leu (Pro54Leu) and its torsion angle changed from －40.2° to －50.4°, which may be conducive to the “lid” domain shift in catalysis for the formation of closed conformation and thus the enzyme-substrate binding becomes more stable. The side chain of Leu54 stretch out to package —SH group exposed to protein surface might keep enzyme activity, and change the pKa value of protein C-terminal Tyr491 resulting in a decrease of the pKa of the active site and shifting the optimum pH to 3.5.

Key words: glutathione synthase, Saccharomyces cerevisiae Y518, nitrosoguanidine, acid resistance