The influence of lipid composition and lectin-glycophorin interaction on the rotational diffusion of glycophorin in vesicles, as measured by time-resolved phosphorescence depolarization.
The rotational mobility of glycophorin in various lipid vesicles was studied, using time-resolved measurements of the depolarization of laser flash excited phosphorescence of glycophorin labelled with the triplet probe erythrosin. With the exception of dimyristoylphosphatidylcholine at the phase transition no phosphorescence depolarization decays were observed in the 1-300 microseconds time interval following the laser flash. Instead, a constant anisotropy level was observed, with two distinct values depending on the experimental system. In liquid-crystalline bilayers of dioleoylphosphatidylcholine, bovine brain phosphatidylserine and dimyristolyphosphatidylcholine, the anisotropy was 0.01. This was increased to 0.03 upon addition of wheat germ agglutinin which aggregates glycophorin. In the case of gel state dimyristoylphosphatidylcholine and liquid-crystalline dioleoylphosphatidylethanolamine the anisotropy also amounted to 0.03. Experiments with glycerol to vary the viscosity of the medium, and theoretical considerations, exclude the possibility that these different anisotropy levels are related to differences in motional properties of the entire protein/lipid vesicles. These results strongly suggest that the anisotropy level of 0.03 corresponds to slowly rotating glycophorin (rotational relaxation time greater than 0.3 ms) while the anisotropy level of 0.01 corresponds to fast rotating glycophorin (rotational correlation time less than 1 microseconds). The difference in glycophorin mobility is discussed in terms of aggregation state of the protein, lipid composition of the vesicle bilayer and membrane viscosity. The observed differences in rotational mobility of glycophorin in glycophorin/dioleoylphosphatidylcholine vesicles, glycophorin/bovine heart phosphatidylserine vesicles as compared to glycophorin/dioleoylphosphatidylethanolamine vesicles are not in quantitative agreement with the relative size of the intramembrane particles in these systems as revealed by freeze-fracture electron microscopy.
D000818:Animals; D002417:Cattle; D004912:Erythrocytes / Q000032:analysis; D006021:Glycophorins / Q000378:metabolism*; D006801:Humans; D007834:Lasers; D037102:Lectins / Q000378:metabolism*; D008055:Lipids / Q000032:analysis*; D008163:Luminescent Measurements; D009904:Optical Rotation; D010713:Phosphatidylcholines / Q000032:analysis; D010714:Phosphatidylethanolamines / Q000032:analysis; D010718:Phosphatidylserines / Q000032:analysis; D012795:Sialoglycoproteins / Q000378:metabolism*; D014909:Wheat Germ Agglutinins
D006021:Glycophorins; D037102:Lectins; D008055:Lipids; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010718:Phosphatidylserines; D012795:Sialoglycoproteins; D014909:Wheat Germ Agglutinins