RESUMO
The specific activity and enantioselectivity of immobilized cutinases from Aspergillus oryzae (AoC) and Humicola insolens (HiC) were compared with those of lipases from Thermomyces lanuginosus (TLL), Rhizomucor miehei (RML) and Lipase B from Candida antarctica (CALB) for menthol and its analogs that include isopulegol, trans-2-tert-butylcyclohexanol (2TBC), and dihydrocarveol (DHC). Common features of these alcohols are two bulky substituents: a cyclohexyl ring and an alkyl substituent. Dissimilarities are that the alkyl group reside at different positions or have dissimilar structures. The aim was to develop an understanding at a molecular level of similarities and differences in the catalytic behavior of the selected cutinases and lipases as a function of substrate structural elements. The experimental results reflect the (-)-enantioselectivity for AoC, HiC, TLL, and RML, while CALB is only active on DHC with (+)-enantioselectivity. In most cases, AoC has the highest activity while HiC is significantly more active than other enzymes on 2TBC. The E values of AoC, HiC, TLL, and RML for menthol are 27.8, 16.5, 155, and 125, respectively. HiC has a higher activity (>10-fold) on (-)-2TBC than AoC while they exhibit similar activities on menthol. Docking results reveal that the bulky group adjacent to the hydroxyl group determines the enantioselectivity of AoC, HiC, TLL, and RML. Amino acid residues that dominate the enantioselectivity of these enzymes are AoC's Phe195 aromatic ring; HiC's hydrophobic Leu 174 and Ile 169 groups; TLL's ring structures of Trp89, His258 and Tyr21; and Trp88 for RML. Results of this study highlight that cutinases can provide important advantages relative to lipases for enantioselective transformation, most notably with bulky and sterically hindered substrates.
