Cell adhesion molecules subunit function

Four Nayl (3-subunits have been cloned and functionally expressed ( 3l-f34) [14-17]. All contain a single membrane-spanning domain and are highly glycosylated. At least some (i-subunits also appear to function as cell adhesion molecules [18]. The (32- and (14-subunils form disulfide bridges... 

Na channel P subunits, the Drosophila Na channel auxiliary subunit TipE, and the P subunits of voltage-gated K and Ca channels have similar functions in terms of modulation of channel activity (Adelman 1995, Isom et al 1994, Warmke et al 1997). As will be discussed below, however, only the mammalian Na channel P subunits also function as cell adhesion molecules (CAMs). What other proteins associate with Na channels and contribute to the ion conduction proteome in excitable cells How is Na channel function affected by these associated proteins and by the local cellular environment Recent advances, outlined below, have begun to answer these important questions in channel biology. 

Evans, J.P., Schultz, R.M., and Kopf, G.S. (1997). Characterization of the binding of recombinant mouse sperm fertilin d subunit to mouse eggs Evidence for function as a cell adhesion molecule in sperm-egg binding. Dev Biol. 757 94-106. 

The / 2-subunit isoform seems to have a function as a recognition element for cell adhesion in the brain. This association may also mediate fine regulation of transport because antibodies to the pi subunit (AMOG = association molecule of glia) cause dissociation of cell-cell adhesion and stimulate Na,K-transport [51]. 

Integrins are a family of transmembrane heterodimeric glycoproteins that are receptors for specific epitopes of extracellular matrix proteins and for other cell-surface molecules (Kramer et al, 1993). Integrins exist as a dimer complex composed of an a-subunit (120-180 kD) noncovalently associated with a /1-subunit (90-110 kD) (Hynes, 1992). At least 8 /1-subunits and 14 -units have been identified and are concentrated at loci, called focal adhesion sites, of close proximity between cells and extracellular matrices on substrates (Hynes, 1992). Focal adhesion sites are points of aggregation of, and are physically associated with, intracellular cytoskeletal molecules that control, direct, and modulate cell function in response to extracellular signals (Schwartz, 1992). 

Fibronectin is an adhesion protein like laminin, vitronectin, and von Wille-brand factor, which are synthesized by the cells themselves to build up the ECM. The glycoprotein fibronectin with a molecular weight between 220,000 and 250,000 consists of two similar subunits, which are connected close to their C-terminus by disulfide bridges. The subunits are composed of functional domains [121]. The cell binding domain with the characteristic sequence Gly-Arg-Gly-Asp-Ser (GRGDS) is of special interest [122]. Models of the subunit of the fibronectin molecule and its cell binding domain are presented in Fig. 21. 

---