Substitution of Ser113 for Gly113 in the cap domain of hydroxynitrile lyase from Manihot esculenta ( MeHNL) was performed by site-directed mutagenesis to improve its self-generated folding and stability under denaturation conditions. The yield of the recombinant mutant HNL1 ( mut-HNL1), which had higher specific activity than the wild type HNL0 (wt-HNL0), was increased by 2 to 3-fold. Thermostability of MeHNL was also enhanced, probably due to an increase in content of the beta-strand secondary structure according to CD analysis. Our data in this report suggest that Ser113 significantly contributes to the in vivo folding and stability of MeHNL and demonstrates an economic advantage of mut-HNL1 over the wt-HNL0.