Characterization of concanavalin A-binding neuronal and glial surface glycoproteins from human foetal brain

Neuronal and glial surface glycoproteins have been isolated from human foetal brains by affinity chromatography on 8 M urea or 6 M guanidine-treated Con A-Sepharose 4B at 4 degrees C and three groups of glycoproteins of molecular mass 65-73 kDa, 52-63 kDa and 43-48 kDa have been identified on SDS/PAGE. These glycoproteins exhibited anomalous behaviour on SDS/PAGE, indicating the existence of a gradation of mutually interconvertible protein-SDS aggregates in dynamic equilibrium with one another. Deglycosylation and deacylation did not alter the SDS/PAGE multiple band pattern. Purified glycoproteins contained 160 +/- 90 micrograms carbohydrate/mg protein, and a sialic acid content of 25 +/- 5 nmole/mg protein. The N-terminals were blocked. The glycoproteins moved preferentially on acid/urea/PAGE. Sepharose 6B gel filtration in the absence of lipid and detergents resolved the glycoproteins into an excluded peak I and a low molecular mass peak II. Peaks I and II were non-interconvertible on Sepharose 6B gel filtration or on reversed phase HPLC in an isopropanol/water/TFA gradient system. Both peaks rendered a single fast moving band of identical mobility on acid/urea/PAGE, suggesting that peak I was possibly a micellar aggregate of the monomeric peak II. The glycoproteins were refractory to digestion by trypsin or pronase and reacted identically towards various lectins.(ABSTRACT TRUNCATED AT 250 WORDS)