The N-linked HNK-1 carbohydrate expressed by several recognition molecules mediates the adhesion of early postnatal cerebellar neurons to the G2 domain of the terminal globular domain of the laminin α1 chain (H.Hall et al., submitted). To define this binding site more precisely, G2-derived synthetic peptides were used for binding and competition studies. Peptide 5-G2, comprising the amino acid residues 3431-3451 of G2, inhibited the interaction between the HNK-1-carrying glycolipid and laminin in a concentrationdependent and saturable manner. Peptides which overlap only partially with this sequence interfered less. Peptides comprising other amino acid sequences from G2, and peptides derived from G1 and G3 or a scrambled version of peptide 5-G2, did not show significant effects. Direct binding of peptide 5-G2 to the HNK-1 glycolipid was also demonstrated. Furthermore, peptide 5-G2 interfered in a concentration-dependent and saturable manner with the adhesion of early postnatal cerebellar neurons to laminin. These observations indicate that amino acid residues 3431-3451 of the laimnin G2 domain are involved in HNK-1 carbohydratemediated cell adhesio
