[Lysosomal hydrolases have specific conformational domains for acquisition of mannose-6-phosphate]

In many mammalian cells, the transport of newly synthesized or externally added lysosomal enzymes to lysosomes is depend on their specific recognition by receptors for mannose 6-phosphate (Man-6-P). The physiological importance of this pathway was confirmed by the finding that fibroblasts from patients with mucolipidosis type II (ML-II ; I - cell disease) fail to phosphorylate mannose residues on their newly synthesized lysosomal enzymes, which results in the secretion of a large percentage of their acid hydrolases into the culture medium. However, lysosomal enzymes themselves do not contain the any consensus amino acid sequences for acquiring the Man-6-P recognition marker. Kornfeld et al revealed using cathepsin D-pepsinogen chimera proteins that UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase recognizes not only oligosaccharides but also the three-dimensional structure of the lysosomal enzymes when transfers N-acetylglucosamine-1-phosphate to lysosomal acid hydrolases.