Integrating Terminal Truncation and Oligopeptide Fusion for a Novel Protein Engineering Strategy To Improve Specific Activity and Catalytic Efficiency: Alkaline α-Amylase as a Case Study

In this work, we integrated terminal truncation and N-terminal oligopeptide fusion as a novel protein engineering strategy to improve specific activity and catalytic efficiency of alkaline alpha-amylase (AmyK) from Alkalimonas amylolytica. First, the C terminus or N terminus of AmyK was partially truncated, yielding 12 truncated mutants, and then an oligopeptide (AEAEAKAKAEAE AKAK) was fused at the N terminus of the truncated AmyK, yielding another 12 truncation-fusion mutants. The specific activities of the truncation-fusion mutants AmyK Delta C500-587::OP and AmyK Delta C492-587::OP were 25.5- and 18.5-fold that of AmyK, respectively. The k(cat)/K-m was increased from 1.0 x 10(5) liters.mol(-1).s(-1) for AmyK to 30.6 x and 23.2 x 10(5) liters.mol(-1).s(-1) for AmyK Delta C500-587::OP and AmyK Delta C492-587::OP, respectively. Comparative analysis of structure models indicated that the higher flexibility around the active site may be the main reason for the improved catalytic efficiency. The proposed terminal truncation and oligopeptide fusion strategy may be effective to engineer other enzymes to improve specific activity and catalytic efficiency.