title: Topographic localization of the heparin-binding domain of the neural cell adhesion molecule N-CAM.
abstract: Previous studies have reported that the cell-binding region of the neural cell adhesion molecule (N-CAM) resides in a 65,000-D amino-terminal fragment designated Frl (Cunningham, B. A., S. Hoffman, U. Rutishauser, J. J. Hemperly, and G. M. Edelman, 1983, Proc. Natl. Acad. Sci. USA, 80:3116-3120). We have reported the presence of two functional domains in N-CAM, each identified by a specific mAb, that are required for cell-cell or cell-substratum adhesion (Cole, G. J., and L. Glaser, 1986, J. Cell Biol., 102:403-412). One of these domains is a heparin (heparan sulfate)-binding domain. In the present study we have determined the topographic localization of the heparin-binding fragment from N-CAM, which has been identified by our laboratory. The B1A3 mAb recognizes a 25,000-D heparin-binding fragment derived from chicken N-CAM, and also binds to a 65,000-D fragment, presumably Frl, produced by digestion of N-CAM with Staphylococcus aureus V8 protease. Amino-terminal sequence analysis of the isolated 25,000-D heparin-binding domain of N-CAM yielded the sequence: Leu-Gln-Val-Asp-Ile-Val-Pro-Ser-Gln-Gly. This sequence is identical to the previously reported amino-terminal sequence for murine and bovine N-CAM. Thus, the 25,000-D polypeptide fragment is the amino-terminal region of the N-CAM molecule. We have also shown that the B1A3 mAb recognizes not only chicken N-CAM but also rat and mouse N-CAM, indicating that the heparin-binding domain of N-CAM is evolutionarily conserved among different N-CAM forms. Additional peptide-mapping studies indicate that the second cell-binding site of N-CAM is located in a polypeptide region at least 65,000 D from the amino-terminal region. We conclude that the adhesion domains on N-CAM identified by these antibodies are physically distinct, and that the previously identified cell-binding domain on Frl is the heparin-binding domain.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000954:Antigens, Surface / Q000276:immunology / Q000378:metabolism; D001665:Binding Sites; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules; D002642:Chick Embryo; D000939:Epitopes; D006023:Glycoproteins / Q000276:immunology / Q000378:metabolism*; D006493:Heparin / Q000378:metabolism*; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000276:immunology / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D015815:Cell Adhesion Molecules; D000939:Epitopes; D006023:Glycoproteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D006493:Heparin