A molecular and biochemical analysis of the structure of the cyanogenic beta-glucosidase (linamarase) from cassava (Manihot esculenta Cranz)

Abstract

The cyanogenic beta-glucosidase (linamarase) of cassava is responsible for the first step in the sequential break-down of two related cyanoglucosides. Hydrolysis of these cyanoglucosides occurs following tissue damage and leads to the production of hydrocyanic acid. This mechanism is widely regarded as a defense mechanism against predation. A linamarase cDNA clone (pCAS5) was isolated from a cotyledon cDNA library using a white clover beta-glucosidase heterologous probe. The nucleotide and derived amino acid sequence is reported and five putative N-asparagine glycosylation sites are identified. Concanavalin A affinity chromatography and endoglycosidase H digestion demonstrate that linamarase from cassava is glycosylated, having high-mannose-type N-asparagine-linked oligosaccharides. Consistent with this structure and the extracellular location of the active enzyme is the identification of an N-terminal signal peptide on the deduced amino acid sequence of pCAS5.