Lateral movements of membrane glycoproteins restricted by dynamic cytoplasmic barriers

Cell membranes often are patchy, composed of lateral domains. These domains may be formed by barriers within or on either side of the membrane bilayer. Major histocompatibility complex (MHC) class 1 molecules that were either transmembrane- (H-2D^b) or glycosylphosphatidylinositol (GPI)-anchored (Qa2) were labeled with antibody-coated gold particles and moved across the cell surface with a laser optical tweezers until they encountered a barrier, the barrier-free path length (BFP). At room temperature, the BFPs of Qa2 and H-2D^b were 1.7 ± 0.2 and 0.6 ± 0.1 (micrometers ± SEM), respectively. Barriers persisted at 34°C, although the BFP for both MHC molecules was fivefold greater at 34°C than at 23°C. This indicates that barriers to lateral movement are primarily on the cytoplasmic half of the membrane and are dynamic.