CELL-SPECIFIC CONSTRAINTS TO THE LATERAL DIFFUSION OF A MEMBRANE GLYCOPROTEIN

We have previously shown that the lateral diffusion, D, of the class I Major Histocompatibility Complex (MHC) glycoprotein H-2L(d) is constrained by its glycosylation, when expressed in mouse L-cells. Removal of one or more of the 3 N linked olisaccharides of H-2L(d) glycoproteins results in an increase in D. In order to further examine the influence of glycosylation on D, we compared lateral diffusion of H-2L(d) expressed in wild-type CHO cells with lateral diffusion of the same molecule expressed in mutant CHO cells with aberrant surface glycosylation. In addition, we compared lateral diffusion of wild-type and unglycosylated H-2L(d) antigens in these cells. In contrast to the large effect of glycosylation state on lateral diffusion of H-2L(d) in mouse L-cells, there was little effect of glycosylation on lateral diffusion of H-2L(d) in any of the CHO cells. This, together with similar results on hamster class I antigens, indicates that the constraints to D of H-2L(d) and other class I MHC molecules are different in CHO cells than in L-cells. Measurements of lateral diffusion after treatment of cells with cytochalasin D make it clear that interactions between MHC class I molecules and a cytoskeleton are important in reducing the mobile fraction of diffusing molecules, R, though they cannot be shown to directly affect the diffusion coefficient, D.