A new peptide-n⁴-(acetyl-β-glucosaminyl)asparagine amidase from soybean (glycine max) seeds: Purification and substrate specificity

We report here the isolation and characterization of a peptide-N⁴-(acetyl-β-glucosaminyl) asparagine amidase (peptide: N-glycanase) from soybean (Glycine max) seeds. The enzyme was purified to homogeneity with 6.5% yield from defatted soybean meal extract by ion-exchange chromatography, gel filtration, hydroxyapatite chromatography, and hydrophobic chromatography. The purified enzyme, designated PNGase-GM, had the apparent molecular mass of 93 kDa by SDS-PAGE and 90 kDa by gel filtration, indicating this PNGase is a monomeric protein. The enzyme showed maximal activity at pH 4.5-5.0. PNGase-GM was capable of hydrolyzing the β-aspartylglycosylamine linkage (GlcNAcβ1→Asn) of various glycopeptide substrates bearing high-mannose type, hybrid type, and xylose/fucose-containing plant complex type N-glycan units, while this amidase was far less active on the glycopeptides bearing sialylated animal complex-type gl.