PURIFICATION OF A CHITOOLIGOSACCHARIDOLYTIC BETA-N-ACETYLGLUCOSAMINIDASE FROM BOMBYX-MORI LARVAE DURING METAMORPHOSIS AND THE NUCLEOTIDE-SEQUENCE OF ITS CDNA

Three beta-N-acetylglucosaminidase (catalyzing hydrolysis of p-nitrophenyl-beta-D-GlcNAc) were purified from the integument tissue of Bombyx mori larvae during metamorphosis into pupae. The largest enzyme (66 kDa by SDS-PAGE, 126 kDa by gel-filtration chromatography) reacted with chitooligosaccharides to produce GlcNAc. A full-length cDNA encoding this chitooligosaccharidolytic beta-GlcNAcase was isolated. Based on the amino acid sequence deduced from the nucleotide sequence, the pre-beta-GlcNAcase was found to consist of 596 amino acid residues including a characteristic signal peptide of 23 residues and have an M(r) of 68,212. Homology search and limited proteolytic digestion showed that the enzyme has a C-terminal 58-kDa catalytic domain very similar to that of human lysosomal beta-hexosaminidase that is responsible for hydrolyzing gangliosides. Two other enzymes (composed of 58-kDa and 48-kDa polypeptides, respectively) did not hydrolyze chitooligosaccharides, and were not proteolytic fragments from the largest enzyme judged by amino acid sequencing analyses. Natural substrates for the beta-GlcNAcases are unknown.