LDAmy, an α-amylase from Colorado potato beetle (Leptinotarsa decemlineata) with transglycosylation activity

Abstract

Potential of α-amylase from the gut of Leptinotarsa decemlineata (LDAmy) to catalyse transfer reactions was investigated. LDAmy as a component of insect gut extract showed significant transfer activity on reducing-end- and both-end-protected maltoheptamer substrates. Transfer reaction was examined using purified enzyme, 2-chloro-4-nitrophenyl β-d-glucopyranoside as acceptor and starch and maltooligosaccharides as donors. In addition to suitability of various donors, effect of pH and acetonitrile (MeCN) concentration were also studied. The reactions were followed using separation of reaction products by a reversed phase HPLC method. LDAmy catalysed the hydrolysis and transglycosylation of the both-end-protected substrate 4,6-O-benzylidene-4-nitrophenyl β-maltoheptaoside in parallel reactions. Shorter and longer both-end-protected products with degree of polymerization 4–10 were formed. Identification of products was carried out based on HPLC retention time, UV and mass spectra. Ratio of transglycosylation to hydrolysis reached 0.5 in presence of 20% MeCN as organic solvent. Aromatic protecting group at the non-reducing end was favourable for transfer reaction. Lack of the mobile loop and presence of more nonpolar aromatic moieties near to the active site may be the reason for the enhanced transfer activity of LDAmy based on the comparison of the sequence and structure of mammalian and insect-derived α-amylases. Highlights Transferase activity of Colorado potato beetle derived α-amylase LDAmy is presented. Effect of pH and organic co-solvent on transfer reaction of LDAmy were studied. Shorter and longer products were formed from a both-end protected maltoheptamer. The unusual transfer ability was explained by sequence differences of α-amylases.