Lipases from Bacillus thermocatenulatus are a member of superfamily of alpha/beta hydrolase, but there are structural differences between them. In this work, we focused on the alpha5 helix of B. thermocatenulatus lipase (BTL2) which is absent in canonical alpha/beta hydrolase fold. In silico study showed that the alpha5 helix is a region that causes disorder in BTL2 protein. So, the alpha5 helix (residues 131 to 150) has been deleted from the B. thermocatenulatus lipase gene (BTL2) and the remain (Deltaalpha5-BTL2) has been expressed in Pichia pastoris yeast. The alpha5 deletion results in increase of enzyme-specific activity in the presence of tributyrin, tricaproin, tricaprylin, tricaprin, trilaurin, and olive oil (C18) substrates by 1.4-, 1.7-, 2.0-, 1.2-, 1.75-, and 1.95-fold, respectively. Also, deletion leads to increase in enzyme activity in different temperatures and pHs, whereas it did not significantly affect on enzyme activity in the presence of organic solvents, metal ions, and detergents.
Lipases are one of the highest value commercial enzymes as they have broad applications in detergent, food, pharmaceutical, and dairy industries. To provide chimeric Bacillus thermocatenulatus lipase (BTL2), the completely conserved pentapeptide ((1)(1)(2)Ala-His-Ser-Gln-Gly(1)(1)(6)) was replaced with similar sequences ((2)(0)(7)Gly-Glu-Ser-Ala-Gly(2)(1)(1)) of Candida rugosa lipase (CLR) at the nucleophilic elbow region. For this purpose, three mutations including A112G, H113E, and Q115A were inserted in the conserved pentapeptide sequence of btl2 gene. Based on the crystal structures of 2W22, the best structure of opened form of the chimeric lipases were garnered using the MODELLER v9.10 software. The native and chimeric lipases were docked to a set of ligands, and a trial version of Molegro Virtual Docker (MVD) software was used to obtain the energy values. Docking results confirmed chimeric lipase to be better than the native lipase. Following the in silico study, cloning experiments were conducted and expression of native and chimeric btl2 gene in Pichia pastoris was performed. The native and chimeric lipases were purified, and the effect of these mutations on characteristics of chimeric lipase studied and then compared with those of native lipase. Chimeric lipase exhibited 1.6-fold higher activity than the native lipase at 55 degrees C. The highest percentage of both lipases activity was observed at 60 degrees C and pH of 8.0. The ion Ca(2)(+) slightly inhibited the activity of both lipases, whereas the organic solvent enhanced the lipase stability of chimeric lipase as compared with the native lipase. According to the results, the presence of two glycine residues at the conserved pentapeptide region of this chimeric lipase ((1)(1)(2)Gly-Glu-Ser-Ala-Gly(1)(1)(6)) may increase the flexibility of the nucleophilic elbow region and affect the enzyme activity level.
