Model-building study of the combining sites of two antibodies to alpha (1----6)dextran

Models of the Fv portion (containing the variable regions of the heavy and light chains) of two monoclonal anti-alpha (1----6)dextran antibodies, W3129 and 19.1.2, were constructed from amino acid sequences and the known three-dimensional structures of the Fv portions of McPC603 and J539. The modeled combining site of W3129 has a protrusion on one side, formed by the long complementarity-determining region 1 of the light chain and the long complementarity-determining region 3 of the heavy chain, and has a cavity accommodating a glucose moiety. The model of the 19.1.2 site is basically flat with a shallow groove that can accommodate several internal glucose units. These results support the earlier conclusions, from ligand binding data, that W3129 has a cavity-type site, involving the terminal nonreducing glucose residue (endbinder), whereas 19.1.2 has a groove-type site.