Evidence for three populations of the glucose transporter in the human erythrocyte membrane

Glucose transporter 1 (GLUT1) is one of 13 members of the human equilibrative glucose transport protein family and the only glucose transporter thought to be expressed in human erythrocyte membranes. Although GLUT1 has been shown to be anchored to adducin at the junctional spectrin-actin complex of the membrane through interactions with multiple proteins, whether other populations of GLUT1 also exist in the human erythrocyte membrane has not been examined. Because GLUT1 plays such a critical role in erythrocyte biology and since it comprises 10% of the total membrane protein, we undertook to evaluate the subpopulations of erythrocyte GLUT1 using single particle tracking. By monitoring the diffusion of individual AlexaFluor 488-labeled GLUT1 molecules on the surfaces of intact erythrocytes, we are able to identify three distinct subpopulations of GLUT1. While the mobility of the major subpopulation is similar to that of the anion transporter, band 3, both a more mobile and more anchored subpopulation also exist. From these studies, we conclude that similar to 65% of GLUT1 resides in similar or perhaps the same protein complex as band 3, while the remaining 1/3rd are either freely diffusing or interacting with other cytoskeletally anchored membrane protein complexes.