CHARACTERIZATION OF A SULFOGLUCURONYL CARBOHYDRATE-BINDING PROTEIN INTHE DEVELOPING NERVOUS-SYSTEM

The developmentally regulated and stage-specifically expressed HNK-1 c arbohydrate found on sulfoglucuronylglycolipids (SGGLs) and certain gl ycoproteins has been proposed to be involved in neural cell adhesion a nd recognition processes through its interaction with protein ''recept ors.'' We have isolated and purified a similar to 30-kDa SGGL-binding protein (SBP-1) from neonatal rat brain, SBP-1 specifically bound to S GGLs and sulfatide both in solid-phase immunobinding and highperforman ce thin-layer chromatography-immunooverlay assays. N-terminal sequence analysis showed that SBP-1 is similar to an adhesive neurite outgrowt h promoting protein amphoterin. Desulfation of SGGLs resulted in aboli tion of SBP-1 binding. However, chemical modification of glucuronic ac id moiety by either esterification or reduction of the carboxyl group had no effect, suggesting requirement of the carbohydrate-linked sulfa te group for SBP-1 binding. The binding of SBP-1 to SGGLs was specific ally inhibited by HNK-1 antibody but not by other IgM antibodies. The binding of SBP-1 to sulfatide, however, was not inhibited by HNK-1 ant ibody, Heparin, fucoidan, and dextran sulfate (50K) also inhibited the binding of SBP-1 to SGGLs. During development of the rat cerebral cor tex, the level of SEP-I 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 b y HNK-1 antibody, but not by other IgM antibodies, indicating that the binding was mediated through the HNK-1 carbohydrate moiety of the pro teins. The interaction and coexpression of SBP-1 with SGGLs and HNK-1 glycoproteins, during the perinatal brain development, suggest a funct ional role for this protein.