For this model, a poorer fit of model and experimental structure is expected (crystals have been obtained and the structure is currently being solved). FitcE2 has a very long CDR-H3, longer than any in the PDB database, which sould be quite flexible. However, the relatively open conformation has been confirmed by an alanine-scan of the residues indicated in red (Graziella Pedrazzi): only a few residues in the very center of the putative binding site affect the binding constant of the antigen, Fluoresceine. The mutants generated for the alanine scan were used to test the resolving power of the Selective Interactive Phage Technology to enrich the variants with the highest affinity, and to correllate single-molecule binding forces measured by atomic force microscopy with macroscopic on- and off-rates of the antigen