Rational Design for Stabilization and Optimum pH Shift of Serine Protease AprN

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Rational shifting of the optimum pH toward alkalinity and cnhancement of thermostability were investigated using an alkaline protease(optimum pH, 10.5-11.5)from the alkaliphilic Bacillus sp. B21-2. The protease gene(aprN)was cloned and the sequence analysis revealed an open reading frame of 379 amino acids that was composed of a putative signal sequence(27 amino acids), a prosequence(84 amino acids), and a mature enzyme of 268 amino acids(MW26, 700). When Lys-230, which was thought to he Located on the surface of the molecule, was replaced by Arg, the optimum pH range was extended further to the alkaline side(11.5-12.0). Also, when the β-turn positions, Ala-38, Ala-165, and Ala-187, were replaced by Pro, the residual activities of the resultant mutant enzymes treated at 55℃ for 30 min were higher than that of the wild-type enzyme(60% as against 30%). These findings suggest that increasing the content of Are residues and reducing the number of Lys residues increases the alkalinity of serine protease, while the introduction of a Pro residue into the β-turn structure stabilizes the enzyme.
社団法人日本生物工学会の論文
1998-01-25