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

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Abstract
Synaptic junctional complexes from rat brain contain 3 major classes of glycoproteins which react with concanavalin A. They have apparent MW 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. They 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. The individual glycoproteins, partially purified by affinity chromatography on concanavalin A-agarose followed by polyacrylamide gel electrophoresis, were reacted. 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. The lectin apparently reacted primarily with polymannose Asp linked oligosaccharides. Each of the glycoproteins 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-labeled concanavalin A positive glycoproteins on wheat germ Sepharose resolved GP 110 and GP 180 into wheat germ positive and negative components. Some structural heterogeneity within these MW classes must exist.