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Enhancing Penicillin G Acylase Stability by Site-directed Mutagenesis.

To improve the stability of penicillin G acylase(PGA) from Bacillus megaterium, a three-dimensional model of B.megaterium PGA was constructed based on crystal structure of penicillin G acylase from E.coli using PMODELING program. The mutation of Lys at beta427 and 430 to Ala was predicted to enhance the stability of PGA in acidic or organic solvent environment. The results showed that 2 mutant PGA had similar specific activity and Km as the parent PGA. Their optimum pH dropped 0.5 pH units. The stability of Lys430Ala was enhanced obviously at pH 5.2. The half lives of Lys427Ala and Lys430Ala were improved by 60 % and 166 %, respectively, in comparison with the parent PGA.