J. Biol. Chem., Vol. 261, Issue 14, 6326-6331, 05, 1986
Phosphorylation of the oligosaccharide of uteroferrin by UDP- GlcNAc:glycoprotein N-acetylglucosamine-1-phosphotransferases from rat liver, Acanthamoeba castellani, and Dictyostelium discoideum requires alpha 1,2-linked mannose residues
R Couso, L Lang, RM Roberts and S Kornfeld
We have investigated the oligosaccharide requirements of the UDP-
GlcNAc:glycoprotein N-acetylglucosamine-1-phosphotransferases from rat
liver, Acanthamoeba castellani, and Dictyostelium discoideum. Uteroferrin,
an acid hydrolase, was phosphorylated by the three N-
acetylglucosaminylphosphotransferases, and the phosphorylated
oligosaccharides were isolated and analyzed by ion suppression high
performance liquid chromatography. In all three cases, the phosphorylated
species contained 6 or more mannose residues. Phosphorylation of the
Man5GlcNAc2 oligosaccharide could not be detected even though this was the
major species on the native uteroferrin. The Man5GlcNAc2 oligosaccharides
lack alpha 1,2-linked mannose residues, whereas the larger oligosaccharides
contain 1 or more mannose residues in this linkage. Treatment of intact
uteroferrin with an alpha 1,2-specific mannosidase-generated molecules
whose oligosaccharides consisted almost entirely of species with 5 mannose
residues. The N-acetylglucosaminylphosphotransferases could no longer
phosphorylate such molecules. These data indicate that at least 1 alpha
1,2-linked mannose residue must be present on uteroferrin's oligosaccharide
for phosphorylation to occur.