Molecular cloning and expression in Pichia pastoris of a Irpex lacteus exo-beta-(1-->3)-galactanase gene.

A gene encoding exo-beta-(1-->3)-galactanase from Irpex lacteus was cloned by reverse transcriptase-PCR. The deduced amino acid sequence showed high similarity with exo-beta-(1-->3)-galactanases from other sources. The molecular mass of the mature form was calculated to be 45,520 Da. The gene product expressed in Pichia pastoris specifically hydrolyzed beta-(1-->3)-galactooligosaccharides, as did other exo-beta-(1-->3)-galactanases. The recombinant enzyme showed high activity toward arabinogalactan-proteins (AGPs) from radish as well as beta-(1-->3)-galactan. Product analysis revealed that the enzyme released beta-(1-->6)-galactobiose, beta-(1-->6)-galactotriose, and alpha-L-arabinofuranosyl-(1-->3)-beta-galactosyl-(1-->6)-galactose together with Gal from beta-(1-->3)-galactans attached with and without beta-(1-->6)-galactosyl branches prepared from acacia gum. These results indicate that the exo-beta-(1-->3)-galactanase from I. lacteus efficiently hydrolyzes beta-(1-->3)-galactan main chains of AGPs by bypassing beta-(1-->6)-galactosyl side chains.