Studies of the synthesis, structure and function of the phosphorylated oligosaccharides of lysosomal enzymes.

Newly synthesized lysosomal enzymes were found to contain N-acetylglucosamine residues in phosphodiester linkage to the 6 position of the mannose residues on high-mannose type oligosaccharides. The formation of these structures was shown to be catalyzed by a specific N-acetylglucosaminylphosphotransferase enzyme, that utilises UDP-N-acetylglucosamine as a donor. The phosphorylation reaction can take place on any of four or five positions on the high-mannose oligosaccharide. Subsequently an α-N-acetylglucosaminylphosphodiesterase removes the outer blocking Nacetylglucosamine residues to generate the mature phosphomannsoyl recognition signal. This signal is responsible for the targetting of newly synthesized lysosomal enzymes to lysosomes. The human syndromes of I-cell disease (Mucolipidosis II) and pseudo-Hurler polydystrophy (Mucolipidosis III) were shown to be caused by deficiency of the first enzyme in the pathway, the UDP-N-acetylglucosamine: Glycoprotein N-acetylglucosaminylphosphotransferase.