Antibody binding sites provide an adaptable surface capable of interacting
with essentially any molecular target. Using CDR shuffling, residues import
ant for the assembly of mucin-1 specific paratopes were defined by random r
ecombination of the complementarity determining regions derived from a set
of mucin-1 specific clones, previously selected from an antibody fragment l
ibrary. It was found that positions 33 and 50 in the heavy chain and 32, 34
, 90, 91 and 96 in the light chain were conserved in many of the clones. Th
ese particular residues seem to be located centrally in the binding site as
indicated by a structure model analysis. The importance of several of thes
e conserved residues was supported by their presence in a mouse monoclonal
antibody with a known structure and the same epitope specificity. Several o
f these corresponding residues in the mouse monoclonal antibody are known t
o interact with the antigen. In conclusion, critical residues important for
maintaining a human antigen-specific binding site during the process of in
vitro antibody evolution were defined. Furthermore, an explanation for the
observed restricted germline gene usage in certain antibody responses agai
nst protein epitopes is provided.