Sialic acid residues on NGF receptors on PC12 cells

Nerve growth factor (NGF) binding to cell surface receptors on PC12 cells is altered by the lectin wheat germ agglutinin (WGA), indicating that the receptor is a glycoprotein. Treatment of PC12 cells with most sugar-specific glycosidases does not substantially affect the ability of the receptor to bind NGF. High concentrations of N-acetyl-D-glucosaminidase (EC 3.2.1.30), however, decreased binding by 20-30%. The ratio of high- and low-affinity binding on PC12 cells also was not affected by glycosidase treatment. However, cleavage of sialic acid residues with neuraminidase (EC 2.3.1.18) increased the mobility of the NGF-receptor complex in a sodium dodecyl sulfate polyacrylamide gel under reducing conditions. Covalent cross-linking of 125I-NGF to PC12 cells reveals the presence of two hormone-receptor complexes with molecular weights of 158,000 and 100,000 daltons, both of which underwent an 10,000 dalton apparent molecular weight decrease after neuraminidase exposure. Neuraminidase also affected the interaction of WGA with the receptor. WGA converted rapidly dissociating NGF binding into a slowly dissociating form, an effect which was inhibited by 50% by prior treatment with neuraminidase. Furthermore, a succinylated derivative of WGA, which binds N-acetyl-D-glucosamine but not sialic acid residues, unlike the native lectin, did not change the kinetic properties of the receptor. These results indicate that NGF receptors contain sialic acid residues which can interact with WGA producing in a change in receptor-binding properties.