Subcellular distribution and partial characterization of the three major classes of concanavalin A receptors associated with rat brain synaptic junctions.

Synaptic junctional complexes from rat brain contain three major classes of glycoproteins which react with concanavalin A. They have apparent molecular weights of 110,000 (GP 110) 130,000 (GP 130), and 180,000 (GP 180). They are present in postsynaptic densities but are not found in microsomes, axolemma, synaptic vesicles, or myelin and are present in low concentrations in the Triton X-100 extract obtained during the preparation of synaptic junctions suggesting that they are uniquely localized to the postsynaptic apparatus. Reaction of the individual glycoproteins, partially purified by affinity chromatography on concanavalin A-agarose followed by polyacrylamide gel electrophoresis, showed that GP 130 contained the most receptor sites for concanavalin A per unit of protein followed by GP 180 and GP 110. Of the receptor sites for concanavalin A, 60-70% were subject to hydrolysis by endoglycosidase H indicating that the lectin reacts primarily with polymannose asparagine linked oligosaccharides. Each of the glycoproteins also reacted to varying degrees with the lectins from Lotus tetragonolobus (specific for alpha-L-fucose), wheat germ (N'-acetyl-D-glucosamine and (or) sialic acid), and lentils (mannose, N'-acetyl-D-glucosamine). Chromatography of 125I-labelled concanavalin A positive glycoproteins on wheat germ Sepharose resolved GP 110 and GP 180 into wheat germ positive and negative components indicating the presence of some structural heterogeneity within these molecular weight classes.