Characterization of the kinetics of neural cell adhesion molecule homophilic binding

Abstract

A solid-phase assay has been developed for the investigation of the kinetics of neural cell adhesion molecule (NCAM) binding. Using this assay we can show that NCAM binds to itself in a time-dependent and saturable manner. Binding constants (KB values) of 6.9 x 10 -s M and 1.23 x 10 -~ M, respectively, were obtained for adult and newborn rat NCAM homophilic binding. Binding is specifically inhibited by Fab' fragments of polyclonal anti-NCAM antibodies but is unaffected by heparin or ehondroitin sulphate. This indicates that the NCAM homophilic binding site is separate from and independent of the heparin-binding site and that a developmental modification, probably polysialation, gives rise to marked differences in the adhesive properties of NCAM.

Interaction between the zinc(II) and the heparin binding site of the Alzheimer's disease βA4 amyloid precursor protein (APP)

“…More rigorous measurements revealed the apparent dissociation constant derived from Scatchard transformation as 3 x 10 -1° M for APP-binding to heparin-Sepharose. This is in good agreement with Kd values obtained by analysis of the binding of heparin to membranes isolated from LX-1 cells [28] but is approximately 60 times lower than that for binding of NCAM to heparin and even lower than that for homophilic binding of NCAM to NCAM [29]. APP binding to heparin in vitro suggests that APP growth stimulation may be mediated through this heparin-binding site in vivo.…”

Structural requirements for neural cell adhesion molecule-heparin interaction.

“…However, kinetic analyses of NCAM-heparin binding and NCAM homophilic interaction have also given conflicting results. One study suggests that NCAM-NCAM binding is not inhibitable by added soluble heparin, although the ionic strength of the incubation buffer used to measure NCAM-heparin binding may have been too high to permit NCAM-heparin binding in vitro (Moran and Bock, 1988). Another study suggests that NCAM-heparin binding occurs more rapidly than NCAM-NCAM binding (Nybroe et al, 1989).…”

Evidence for the presence of N‐CAM 180 on astrocytes from rat cerebellum and differences in glycan structures between N‐CAM 120 and N‐CAM 140

“…Although the structure of Nlinked oligosaccharides of N-CAM has not be analyzed in detail, the presence of two novel carbohydrate residues in the outermost position of the glycan of N-CAM has been determined to be important functionally. Polysialic acid (homopolymer of Sia␣2=8 linkage) is a unique carbohydrate moiety on N-CAMs and is known to modify the affinity of N-CAM (Moran and Bock, 1988). On the other hand, HNK-1 epitope (3-sulfated glucuronic acid) is present on a variety of CAMs, including N-CAMs, and is considered to be important in various cellular interactions (Kruse et al, 1984;Cole and Schachner, 1987;Kü nemund et al, 1988).…”