Glycosylation of the human erythrocyte glucose transporter is essential for glucose transport activity

The human erythrocyte glucose transporter is a fully integrated membrane glycoprotein having only one N-linked carbohydrate chain on the extracellular part of the molecule. Several authors have suggested the involvement of the carbohydrate moiety in glucose transport, but not definitive results have been published to date. Using transport glycoproteins reconstituted in proteoliposomes, kinetic studies of zero-trans influx were performed before and after N-glycanase treatment of the proteoliposomes: this enzymatic treatment results in a 50% decrease of the Vmax. The orientation of transport glycoproteins in the lipid bilayer of liposomes was investigated and it appears that about half of the reconstituted transporter molecules are oriented properly. Finally, it could be concluded that the release of the carbohydrate moiety from the transport glycoproteins leads to the loss of their transport activity.