Surface charged amino acid-based strategy for rational engineering of kinetic stability and specific activity of enzymes: Linking experiments with computational modeling.

Abstract A rational workflow for engineering kinetically stable enzymes with good specific activity by surface charged amino acids engineering was proposed based on systematically analyzing the results of mutating 44 negatively charged surface amino acids of a thermophilic β-mannanase (ManAK). Computational data, combined with experimental results indicated that percentage side-chain solvent accessibility (PSSA), changes in Gibbs free energy of unfolding (∆∆Gmut) and root-mean-square fluctuations (RMSF) could be suitable for screening kinetically stable mutants. A combinational standard (∆∆Gmut  0.68 A) resulted a decrease in the proportion of destabilizing mutants to 12.5%. The perturbations of substrate affinity and specific activity caused by mutation were weakened as the shortest distance from Cα of mutated site to Cα of catalytic sites (DsCα-Cα) increased. Results indicated that hotspot zones contributing to the local stability and integrity of catalytic motif at elevated temperatures might be widely distributed across spatial structure of the protein, while the mutation perturbation on enzyme specific activity demonstrated a gradually weakening trend from the catalytic core to the protein surface. These findings further our understanding of the structural-functional relationships of protein and highlight a deduced workflow to engineering industrially useful enzymes.