Model-building Studies of Antigen-binding Sites: The Hapten-binding Site of MOPC-315

The molecular basis for the structural diversity of antibody combining sites has become apparent through the recent X-ray diffraction studies on several immunoglobulin (Ig) fragments (see Davies et al. 1975a,b for a review). These structures reveal that the combining site is formed by bringing together the three hypervariable regions (Wu and Kabat 1970) of VL and of VH to form a continuous complementarity-providing surface. A quantitative comparison of the tertiary structures of a number of variable domains from both light and heavy chains has demonstrated that their nonhypervari-able or framework regions are very similar, with the principal differences occurring in the hypervariable loops (Padlan and Davies 1975).