Antigen binding

Four possible mechanisms for solid-state extraction (a) adsorption onto a solid substrate (b) absorption into a thin polymer or chemical film coated on a solid substrate (c) metal-ligand complexation in which the ligand is covalently bound to the solid substrate and (d) antibody-antigen binding in which the receptor is covalently bound to the solid substrate. 

The antigen-binding site is formed by close association of the hypervariable regions from both heavy and light chains... 

The variable domains associate in a strikingly different manner. It is obvious from Figure 15.11 that if they were associated in the same way as the constant domains, via the four-stranded p sheets, the CDR loops, which are linked mainly to the five-stranded p sheet, would be too far apart on the outside of each domain to contribute jointly to the antigen-binding site. Thus in the variable domains the five-stranded p sheets form the domain-domain interaction area (Figure 15.11). Furthermore, the relative orientation of the p strands in the two domains is closer to parallel than in the constant domains and the curvature of the five-stranded p sheets is such that they do not pack... 

The antigen-binding site binds haptens in crevices and protein antigens on large flat surfaces... 

MHC molecules are composed of antigen-binding and immunoglobulin-like domains... 

Figure 15.19 Schematic representation of the peptide-binding domain of a class I MHC protein. The al and a2 domains are viewed from the top of the molecule, showing the empty antigen-binding site as well as the surface that is contacted by a T-cell receptor. (Adapted from P.J. Bjdrkman et al.. Nature 329 506-512, 1987.)...

T-cell receptors (TCR) are heterodimeric transmembrane glycoproteins found exclusively in T cells, with extracellular domains that closely resemble antibody Fab structures. Each of the TCR a and p chains forms half of an extracellular antigen-binding domain, and in addition has one transmembrane... 

Segal, D.M., et al. The three-dimensional structure of a phosphorylcholine-binding mouse immunoglobulin Fab and the nature of the antigen-binding site. Proc. Natl. Acad. Sci. USA 71 4298-4302, 1974. 

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