Oriented irreversible immobilization of a glycosylated Candida antarctica B lipase on heterofunctional organoborane-aldehyde support

Abstract

The immobilization of Candida antarctica (fraction B) lipase expressed in Pichia pastoris, a selective glycosylated protein at Asn 74, on a new heterofunctional support consisted of phenylboronic acid and aldehyde groups (Borald) has been performed. This method occurs via a two step mechanism: first orientation by organoborane interaction at neutral pH and a consecutive multi-point covalent attachment by aldehyde reaction at alkaline pH. The enzyme was specifically immobilized on this support in 70% yield at pH 7, oriented by the reaction of the hydroxyl groups on the sugar moiety with boronic acid on the support, whereas commercial CAL-B from Novozymes (non-glycosylated) was hardly immobilized at this pH (<10%). The consecutive incubation at pH 10 permitted the reaction of amine groups of the protein with aldehyde groups on the support. After a reductive amination, an irreversible immobilization methodology on organoborane-aldehyde support was possible with >99% final immobilization yield. The Borald-CAL-B preparation was a very stable biocatalyst in the presence of high amount of solvent or high temperature (e.g. more than 10 fold in the presence of 60% (v/v) acetonitrile). An improvement of the specific activity up to 5 fold for example in the hydrolysis of methyl phenyl acetate was obtained compared with a one-point covalent preparation. An ee of 89% towards R isomer was achieved with this new immobilized biocatalyst in the enantioselective hydrolysis of methyl mandelate.