Role of Q177A and K173A/Q177A substitutions in thermostability and activity of the ELBn12 lipase.

Thermostable lipases have many applications in detergent industries and in organic synthesis. There are many ways to improve thermal stability of enzymes, for example, higher hydrophobicity, greater structural packing, higher content of the charged residues, and lower thermolabile ones. In this study, thermolabile Gln (sensitive to higher temperatures) was substituted with Ala in native ELBn12 and mutated K173A lipases to examine its effect on thermal stability and activity of the lipases. Single (Q177A) and double mutants (K173A/Q177A) were expressed in Escherichia coli pLysS. The Q177A variant increased both activity and thermostability of the lipase, whereas K173A/Q177A had a negative effect on the lipase activity and only had better thermal stability than the native at 50 °C. pH stability of the double mutant between 9.0 and 11 was also lower than the other variants. Stability analysis in the presence of chemicals showed that Q177A mutant had better activity with 50% (v/v) organic solvents. On the other hand, K173A lipase showed increased activity with 1% (w/v) nonionic surfactant, and finally K173A/Q177A had better stability with 10 mM metal ions compared to the native lipase.