The immunoglobulin-superfamily molecule basigin is a binding protein for oligomannosidic carbohydrates: an anti-idiotypic approach Martin Heller,* ,1 Maren von der Ohe,  ,1 Ralf Kleene,* M. Hasan Mohajeri* and Melitta Schachner* ,   *Department of Neurobiology, Swiss Federal Institute of Technology, Zu ¨rich, Switzerland  Zentrum fu ¨r Molekulare Neurobiologie, University of Hamburg, Hamburg, Germany Abstract Recognition molecules that carry carbohydrate structures regulate cell interactions during development and play important roles in synaptic plasticity and regeneration in the adult. Glycans appear to be involved in these interactions. We have searched for binding proteins for oligomannosidic structures using the L3 antibody directed against high man- nose-type glycans in an anti-idiotypic approach. A selected monoclonal anti-idiotype antibody was used for affinity chro- matography and identified basigin as a binding protein from mouse brain detergent lysates. Basigin was found to bind to high mannose-carrying cell recognition molecules, such as myelin-associated glycoprotein, L1, the b2-subunit of Na + /K + - ATPase and an oligomannosidic neoglycolipid. Furthermore, basigin was involved in outgrowth of astrocytic processes in vitro. A striking homology between the first immunoglobulin (Ig)-like domain of basigin and the fourth Ig-like domain of NCAM, previously shown to bind to oligomannosidic glycans, and the lectin domain of the mannose receptor confirms that basigin is an oligomannose binding lectin. To our knowledge this is the first report that anti-idiotypic antibodies can be used to identify binding partners for carbohydrates. Keywords: anti-idiotypic antibody, basigin, cell recognition, lectin, nervous system, oligomannosidic glycans. J. Neurochem. (2003) 84, 557–565. Increasing evidence indicates that cell surface carbohydrates and carbohydrate-specific binding proteins, also called lectins, mediate recognition between cells (for review see: Varki 1993; Weis and Drickamer 1996; Muramatsu 2000; Feizi 2001; Furukawa et al. 2001; Helenius and Aebi 2001). Despite the overwhelming evidence that carbohydrates and their respective receptors are involved in cell recognition, direct evidence that oligosaccharides play important func- tional roles in the nervous system has remained relatively sparse. Indirect support for such a function has been derived from the temporally and spatially restricted pattern of expression of cell surface carbohydrates and their putative receptors (for reviews see: Schachner and Martini 1995; Rutishauser 1998; Lander and Selleck 2000). A functional involvement of carbohydrate structures in cell recognition has been demonstrated for the spatially and temporally regulated attachment of polysialic acid to neural cell adhesion molecule NCAM (for review see: Rutishauser 1998). Further examples for carbohydrate structures in the nervous system are the HNK-1, L3, L4 and L5 epitopes which are found on several neural recognition molecules. The L5 epitope, which is identical to the Lewis x -carbohy- drate (Streit et al. 1996), is present on several neural recognition molecules and is involved in extension of astrocytic processes (Streit et al. 1993) and neural induction (Roberts et al. 1991). The HNK-1 carbohydrate structure containing an unusual 3¢-sulfated glucuronic acid (Chou Received May 22, 2002; revised manuscript received October 4, 2002; accepted October 19, 2002. Address correspondence and reprint requests to Melitta Schachner, Zentrum fu ¨r Molekulare Neurobiologie, Martinistr. 52, D-20246 Ham- burg, Germany. E-mail: melitta.schachner@zmnh.uni-hamburg.de 1 These authors contributed equally to this work. Abbreviations used: AMOG, adhesion molecule on glia; BME, basal medium Eagle; BSA, bovine serum albumin; CRD, carbohydrate recognition domains; DSCAM, Down’s syndrome cell adhesion mole- cule; ELISA, enzyme-linked immunosorbant assay; GFAP, glial fibrillary acidic protein; GST, glutathione-S-transferase; Ig, immunoglobulin; MAG, myelin associated glycoprotein; PBS, phosphate buffered saline. Journal of Neurochemistry , 2003, 84, 557–565 Ó 2003 International Society for Neurochemistry, Journal of Neurochemistry , 84, 557–565 557