The α- and β-subunits of the human UDP-N-acetylglucosamine: lysosomal enzyme phosphotransferase are encoded by a single cDNA

Abstract

Lysosomal enzymes are targeted to the lysosome through binding to mannose 6-phosphate receptors because their glycans are modified with mannose 6-phosphate. This modification is catalyzed by UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase). Bovine GlcNAc-phosphotransferase was isolated using monoclonal antibody affinity chromatography, and an α2β2γ 2-s\Anmit structure was proposed. Although cDNA encoding the γ-subunit has been described, cDNAs for the α- and β-subunits have not. Using partial amino acid sequences from the bovine α- and β-subunits, we have isolated a human cDNA that encodes both the α- and β-subunits. Both subunits contain a single predicted membrane-spanning domain. The α- and β-subunits appear to be generated by a proteolytic cleavage at the Lys928-Asp929 bond. Transfection of 293T cells with the α/β-subunits-precursor cDNA with or without the γ-subunit cDNA results in a 3.6- or 17-fold increase in GlcNAc-phosphotransferase activity in cell lysates, suggesting that the precursor cDNA contains the catalytic domain. The sequence lacks significant similarity with any described vertebrate enzyme except for two Notch-like repeats in the α-subunit. However, a 112-amino acid sequence is highly similar to a group of bacterial capsular polymerases (46% identity). A BAC clone containing the gene that spanned 85.3 kb and was composed of 21 exons was sequenced and localized to chromosome 12q23. We now report the cloning of both the cDNA and genomic DNA of the precursor of GlcNAc-phosphotransferase. The completion of cloning all three subunits of GlcNAc-phosphotransferase allows expression of recombinant enzyme and dissection of lysosomal targeting disorders. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.