In insects, beta-N-acetylglucosaminidase (GIcNAcase) participates in critical physiological processes such as fertilization, metamorphosis, and glycoconjugate degradation. Insects produce glycoproteins carrying paucimannosidic-type N-glycans, the terminal GIcNAc residue of which is cleaved by a GIcNAc-linkage specific GIcNAcase, also known as the fused lobes (FDL) protein. To obtain information on the structure of GIcNAcases and insight into their contribution to physiological processes, we cloned Bombyx mori FDL (BmFDL) from silkworm larvae. The full-length cDNA (1.9 kb) encoded a protein of 633 amino acids with 42% amino acid sequence identity to Drosophila melanogaster FDL (DmFDL). Recombinant BmFDL cleaved only beta-1,2-linked GlcNAc residues from the alpha-1,3 branch of biantennary N-glycan. This substrate specificity was similar to that of DmFDL. Microsomal FDL activity was inhibited by anti-BmFDL antibodies. Taken together, our results suggest that BmFDL is a N-glycan-processing GIcNAcase in B. mori. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.