Binding Properties of the Neural Cell Adhesion Molecule to Different Components of the Extracellular Matrix

Abstract

A soluble form of the neural cell adhesion molecule (N-CAM) was obtained from 100,000-g supernatants of crude brain membrane fractions by incubation for 2 h at 37°C. The isolated N-CAM, consisting of one polypeptide chain with a molecular mass of 110 kilodaltons (N-CAM 110), was studied for its binding specificity to different components of the extracellular matrix (ECM). N-CAM 110 bound to different types of collagen (collagen types I-VI and IX). The binding efficiency was dependent on salt concentration and could be called specific according to the following criteria: (a) Binding showed substrate specificity (binding to collagens, but not to other ECM components, such as laminin or fi-bronectin). (b) Binding of N-CAM 110 to heat-denatured collagens was absent or substantially reduced, (c) Binding was saturable (Scatchard plot analyses were linear with K_D values in the range of 9.3-2.0 ± 10⁻⁹M, depending on ihe collagen type and buffer conditions). Binding of N-CAM 110 to collagens could be prevented in a concentration-dependent manner by the glycosaminoglycans heparin and chondroitin sulfate. N-CAM 110 also interacted with immobilized heparin, and this interaction could be prevented by heparin and chondroitin sulfate. Thus, in addition to its role in cell-cell adhesion, N-CAM is a binding partner for different ECM components, an observation suggesting that it also serves as a substrate adhesion molecule in vivo