Comparison of the N-glycosylation sites between the Hex α- and β-subunits by in silico modeling. Three-dimensional structures of the human β-hexosaminidase A are presented. The location of the glycosylation sites in the α- (N115, N157, and N295) and β-subunits (N84, N142, N190, and N324) are presented as space-filling models. The N-glycan carrying M6P residues are attached to N295 in the α-subunit, and to N84 as well as N327 in the β-subunit. Amino acid substitutions (S51N and A53T) in the α-subunit are predicted to cause the additional N-glycan carrying M6P residues, and correspond to those (N84N and T86) in the β-subunit. The yellow circle indicates a novel glycosylation site in the α-subunit.