Molecular topography of the neural cell adhesion molecule N-CAM: surface orientation and location of sialic acid-rich and binding regions.

Abstract

Chemical analyses and binding studies have been correlated to clarify the relationship of structure to function in the neural cell adhesion molecule (N-CAM) from embryonic chicken brain. N-CAM isolated from the cell surface appears to include two closely related polypeptide chains. Treatment with neuraminidase of such preparations of N-CAM bound by antibodies on solid supports yielded components of Mr 140,000 and 170,000. These components each had the same amino-terminal sequence as N-CAM and gave nearly identical profiles on peptide maps. Immunoprecipitation of N-CAM from 9-day brain cells treated with tunicamycin yielded corresponding components of Mr 130,000 and 160,000, suggesting that the differences between these two components of N-CAM are in the polypeptide rather than the carbohydrate portions of the molecules. N-CAM appears to be oriented with the amino terminus extending away from the cell surface and with the bulk of the sialic acid near the middle of the peptide chain. As shown previously, incubation of N-CAM at 37 degrees C generates a fragment (Fr1) of Mr 65,000 that lacks most of the sialic acid. Treatment of membranes with Staphylococcus aureus V-8 protease released a fragment (Fr2) of N-CAM that contained most of the sialic acid; this fragment had an Mr of 108,000 after neuraminidase treatment. Both of these fragments contain the amino-terminal portion of the polypeptide chain. At least a portion of the N-CAM binding site was found to be located in the amino-terminal region of the peptide chain. Most or all of the sialic acid was not directly involved in binding, although it can influence binding, as indicated by the finding that neuraminidase-treated N-CAM (desialylated-N-CAM) bound to cells to a greater extent than untreated N-CAM. The Fr1 and the Fr2 fragments in solution did not bind to cells but were as effective as N-CAM and desialylated-N-CAM as competitors for N-CAM binding to cells. When fixed covalently to beads, N-CAM, desialylated-N-CAM, and the Fr1 and Fr2 fragments bound specifically to cells. In contrast, the N-CAM autolysis products released along with Fr1 neither bound to cells nor competed for N-CAM binding. In addition to suggesting a location for the N-CAM binding region, the accumulated results raise the possibility that valence may play a key role in N-CAM binding.

Neural Cell Adhesion Molecule (N-CAM) Homophilic Binding Mediated by the Two N-terminal Ig Domains Is Influenced by Intramolecular Domain-Domain Interactions

“…The site of flexibility in the EM images lies between Ig4 and Ig5, based on the structures of N-CAM Ig and FnIII domains (19). Supporting evidence for a conformationally sensitive site in this region comes from the observation of a proteolytic fragment from native N-CAM whose size is consistent with cleavage near the Ig4 Ig5 boundary (41). Furthermore, the recombinant fusion proteins lost adhesiveness after several freeze-thaw cycles without obvious signs of degradation.…”

The Role of Sialylated Glycans in Human Platelet Endothelial Cell Adhesion Molecule 1 (PECAM-1)-mediated Trans Homophilic Interactions and Endothelial Cell Barrier Function

“…Although the role of glycans in cell adhesion has been best characterized in the Selectin (31) and sialic acid-binding Ig-like lectins (Siglec) (32) families of glycan-binding proteins, other notable cell adhesion molecules in which carbohydrate residues have been shown to play a prominent role include E-Cadherin (33, 34), neural cell adhesion molecule (35), ICAM-1 (36, 37), vascular cell adhesion molecule (38), and junctional adhesion molecule (39). Despite the fact that the molecular mass of PECAM-1 is ϳ30% carbohydrate (3,19), there have been only a handful of studies examining the potential contribution of PECAM-1-linked glycans to its adhesive and signaling function, and most of these have been performed in murine cells.…”

Learning under stress: A role for the neural cell adhesion molecule NCAM

“…PSA modulates cell-cell interactions through its attachment to NCAM by reducing homo-and heterophilic NCAM adhesive activities (Cunningham, Hoffman, Rutishauser, Hemperly, & Edelman, 1983;Johnson, Fujimoto, Rutishauser, & Leckband, 2005;Rutishauser, 1998;Sadoul, Hirn, Deagostini-Bazin, Rougon, & Goridis, 1983). PSA-NCAM is highly expressed during brain development and its levels gradually decrease during the early post-natal period (Angata & Fukuda, 2003;Rutishauser, 2008).…”