-L-Fucosidase from Bombyx mori has broad substrate specificity and hydrolyzes core fucosylated N-glycans

N-glycans play a role in physiological functions, including glycoprotein conformation, signal transduction, and antigenicity. Insects display both alpha-1,6-and alpha-1,3-linked fucose residues bound to the innermost N-acetylglucosamine of N-glycans whereas core alpha-1,3-fucosylated N-glycans are not found in mammals. Functions of insect core-fucosylated glycans are not clear, and no alpha-L-fucosidase related to the N-glycan degradation has been identified. In the genome of the domestic silkworm, Bombyx mori, a gene for a protein, BmFucA, belonging to the glycoside hydrolase family 29 is a candidate for an alpha-L-fucosidase gene. In this study, BmFucA was cloned and recombinantly expressed as a glutathione-S-transferase tagged protein (GST-BmFucA). Recombinant GSTBmFucA exhibited broad substrate specificity and hydrolyzed p-nitrophenyl alpha-L-fucopyranoside, 2 '-fucosyllactose, 3-fucosyllactose, 3-fucosyl-N,N '-diacetylchitobiose, and 6-fucosyl-N,N '-diacetylchitobiose. Further, GST-BmFucA released fucose from both pyridylaminated complex-type and paucimannose-type glycans that were core-alpha-1,6-fucosylated. GST-BmFucA also shows hydrolysis activity for core-fucosylated glycans attached to phospholipase A2 from bee venom. BmFucA may be involved in the catabolism of core-fucosylated N-glycans in B. mori.