Glucose phosphotransferase and intracellular trafficking.

Glycoproteins containing phosphodiester-linked glucose residues have recently been described. The synthesis of this structure occurs due to the intact transfer of alpha glucose-1-phosphate from UDP-glucose and is catalyzed by the enzyme glucose phosphotransferase (GlcPTase). The endogenous acceptors for GlcPTase have been characterized as to molecular weight following incubation of selected homogenates with (beta 32P)UDP-glucose. These glycoproteins are distinct from the lysosomal hydrolases recognized by the GlcNAc phosphotransferase. The transfer of 32P from (beta 32P)UDP-Glc can also be detected when the nucleotide sugar is microinjected into the cytoplasm of individual neurons in Aplysia. The phosphorylated acceptors in this system seem to be predominantly two glycoproteins that are subjected to rapid axoplasmic transport. The possible role of this post-translational modification in the intracellular trafficking of a subset of newly synthesized glycoproteins is discussed.