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.