Lipases fromRhizomucor miehei andHumicola lanuginosa: Modification of the lid covering the active site alters enantioselectivity

The homologous lipases fromRhizomucor miehei andHumicola lanuginosa showed approximately the same enantioselectivity when 2-methyldecanoic acid esters were used as substrates. Both lipases preferentially hydrolyzed theS-enantiomer of 1-heptyl 2-methyldecanoate (R. miehei:E_S=8.5;H. lanuginosa:E_S=10.5), but theR-enantiomer of phenyl 2-methyldecanoate (E_R=2.9). Chemical arginine specific modification of theR. miehei lipase with 1,2-cyclohexanedione resulted in a decreased enantioselectivity (E_R=2.0), only when the phenyl ester was used as a substrate. In contrast, treatment with phenylglyoxal showed a decreased enantioselectivity (E_S=2.5) only when the heptyl ester was used as a substrate. The presence of guanidine, an arginine side chain analog, decreased the enantioselectivity with the heptyl ester (E_S=1.9) and increased the enantioselectivity with the aromatic ester (E_R=4.4) as substrates. The mutation, Glu 87 Ala, in the lid of theH. lanuginosa lipase, which might decrease the electrostatic stabilization of the open-lid conformation of the lipase, resulted in 47% activity compared to the native lipase, in a tributyrin assay. The Glu 87 Ala mutant showed an increased enantioselectivity with the heptyl ester (E_S=17.4) and a decreased enantioselectivity with the phenyl ester (E_R=2.5) as substrates, compared to native lipase. The enantioselectivities of both lipases in the esterification of 2-methyldecanoic acid with 1-heptanol were unaffected by the lid modifications.