Lectin-mediated agglutination of liposomes containing glycophorin: Effects of acyl chain length

Abstract

Glycophorin from human erythrocytes has been incorporated into liposomes of dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC) and distearoylphosphatidylcholine (DSPC). The thermal properties of unsonicated liposomes with glycophorin/lipid molar ratios up to 4·10 −3 have been studied by differential scanning calorimetry and the numbers of lipids withdrawn from participation in the gel-to-lamellar phase transition were found to be 42±22 (DMPC), 197±28 (DPPC) and 240±64 (DSPC). The initial rates of agglutination of sonicated liposomes with glycophorin/lipid molar ratios up to 4·10 −3 by wheat germ agglutinin in the concentration range 0–7 μM have been measured over a range of temperature. Below the gel-to-lamellar phase transition ( T c) the rates of agglutination increase with acyl chain length in the sequence DMPC < DPPC < DSPC. Agglutination is found to be second order in liposome concentration and is completely reversed on saturation of the wheat germ agglutinin-binding sites by N-acetylglucosamine. Agglutination rates decrease with increasing temperature below T c and are largely independent of temperature above T c. The results are discussed in relation to the clustering of glycophorin in the phospholipid bilayers and its effect on binding and subsequent interliposomal bridge formation by wheat germ agglutinin.