Enhancement of the thermostability of Streptomyces kathirae SC-1 tyrosinase by rational design and empirical mutation

• PoPMuSiC algorithm was applied to predict more thermostable tyrosinase.
• Site-directed mutagenesis was applied to obtain more thermostable tyrosinase.
• Mutants showed 3-fold and 10 °C increase in half-life and optimal temperature.
• The additional hydrogen bonds may be of value to improve the thermostability.
• The improved thermostability may be due to the newly formed favorable interaction.

This study aimed to improve the thermostability of a newly cloned tyrosinase from Streptomyces kathirae SC-1. The POPMuSiC algorithm was applied to predict the folding free energy change (ΔDG) of amino acid substitution. Site-directed mutagenesis was used to construct mutants (Q7K, G234P, and Q7K/G234P), and the mutant, and wild-type enzymes were expressed in Escherichia coli (DE3). Compared to the wild-type tyrosinase, all three mutant enzymes showed improved thermal properties. The mutant with combined substitution (Q7K/G234P) showed the most pronounced shifts in temperature optima, about 10 °C upward, and the half-life for thermal inactivation at 60 °C, and melting temperatures were increased by 3 times and approximately 10 °C, respectively. Finally, the mechanisms responsible for the increased thermostability were analyzed through comparative analysis of structure models. The structure-based rational design strategies in this study may also provide further insight into the thermostability of other industrial enzymes and suggest further potential industrial applications.