Cell adhesion molecules homophilic binding

Adhesion molecules such as LI, neural cell adhesion molecule (N-CAM) and N-cadherin promote axonal regeneration by homophilic interactions between axons and Schwann cell surfaces (see Ch. 7). The expression of p75 (low affinity NGF receptor, Ch. 27) is also increased at the Schwann cell surface after injury. Extracellular matrix molecules, such as tenascin and proteoglycans, increase the regenerative potential of damaged peripheral nerves by binding to integrins on the axonal surface. 

Effects of oligosaccharides on the biological functions of proteins (15 examples). The capacity for homophilic binding of the neural cell adhesion molecule (N-CAM, Section 12.5.3) is modulated by the extension of its polysialic chains. The binding of a highly specific heparin pentasaccharide sequence to the protein antithrombin III converts it to a potent anticoagulant (Section 17.3). 

Soroka, V., Kiryushko, D., Novitskaya, V. et al. 2002. Induction of neuronal differentiation by a peptide corresponding to the homophilic binding site of the second Ig module of the neural cell adhesion molecule./Biol Chem, 277 24676-83. 

Mauro, V.P., Krushel, L.A., Cunningham, B.A., Edelman, G.M. Homophilic and heterophilic binding activities of N-CAM a nervous system cell adhesion molecule. J. Cell Biol, 1992, 119, 191-202. 

Hoffman, S., and Edelman, G. M., 1983, Kinetics of homophilic binding by embryonic and adult forms of the neural cell adhesion molecule, Proc. Natl. Acad. Sci. USA 80 5762-5766. 

The classic cadherins are homophilic adhesion molecules. That is, E-cadherin expressed on one cell surface binds to E-cadherin expressed on an apposed cell surface, N-cadherin binds to N, P to P and so forth. It was originally thought that all cadherins would behave completely homophilically but it is now clear that, for example, N-cadherin can bind to R-cadherin, although perhaps more weakly than it would to N-cadherin. 

Cadherins are Ca -binding adhesion molecules that mediate homophilic interaction between cells. Cadherins are particularly important for selective fasciculation of regenerating axons. For instance, E-cadherin mediates attachment of unmyelinated sensory fibers and stabilizes glial network [42], and N-cadherin mediates axon-Schwann ceU interactions during regeneration [39, 43]. 

Figure 2 Initial adhesion of a human blastocyst to endometrial surface epitheha mediated by trophinin. A human blastocyst secretes glycoprotein hormone, hCG. It is likely that a human blastocyst expresses homophilic adhesion molecule trophinin on the trophectoderm surface at embryonic pole in a similar manner as a monkey blastocyst does (36). When the blastocyst comes close to the endometrial epithelia cells, high concentration of hCG derived from blastocyst affects locally the maternal epithelia (left) and induces trophinin expression in narrowly limited region of endometrial epithelia (center) (38). The blastocyst and endometrial epithelia then adhere to each other through trophinin-trophinin binding (right).

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