The developmentally regulated and stage-specifically expressed HNK-1 carbohydrate found on sulfoglucuronyiglycolipids (SGGLs) and certain glycoproteins has been proposed to be involved in neural cell adhesion and recognition processes through its interaction with protein "receptors." We have isolated and purified ã -~30-kDa SGGL-binding protein (SBP-1) from neonatal rat brain. SBP-1 specifically bound to SGGLs and sulfatide both in solid-phase immunobinding and highperformance thin-layer chromatography-immunooverlay assays. N-terminal sequence analysis showed that SBP-1 is similar to an adhesive neurite outgrowth promoting protein amphoterin. Desulfation of SGGLs resulted in abolition of SBP-1 binding. However, chemical modification of glucuronic acid moiety by either esterification or reduction of the carboxyl group had no effect, suggesting requirement of the carbohydrate-linked sulfate group for SBP-1 binding. The binding of SBP-1 to SGGLs was specifically inhibited by HNK-1 antibody but not by other 1gM antibodies. The binding of SBP-1 to sulfatide, however, was not inhibited by HNK-1 antibody. Heparin, fucoidan, and dextran sulfate (50K) also inhibited the binding of SBP-1 to SGGLs. During development of the rat cerebral cortex, the level of SBP-1 decreased after embryonic day 18 to an almost undetectable level by postnatal day 10; whereas in the cerebellum, the expression of SBP-1 was maximal at postnatal day 7. SBP-1 also bound specifically to the HNK-1 glycoproteins isolated from rat brain by HNK-1 immunoaffinity chromatography. Proteins without HNK-1 carbohydrate did not bind SBP-1. The binding to HNK-1 glycoproteins was inhibited by HNK-1 antibody, but not by other 1gM antibodies, indicating that the binding was mediated through the HNK-1 carbohydrate moiety of the proteins. The interaction and coexpression of SBP-1 with SGGLs and HNK-1 glycoproteins, during the perinatal brain development, suggest a functional role for this protein. Key Words: Sulfoglucuronylglycolipid -Glycoprotein-HNK-1 carbohydrate-Neural cell adhesion and recognition-Binding protein-HNK-1 antibody-Rat brain.
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