Modelling antibody-antigen interactions: ferritin as a case study.

In this work, we propose a model for the structure of the antigen-antibody complex formed by human H-ferritin and an antibody that specifically recognizes it. We cloned and sequenced the antibody gene, predicted the antibody three-dimensional structure, and reconstructed the H-ferritin-antibody complex using an automated docking procedure previously validated on known complexes. This procedure allowed us to identify one putative complex which we carefully analysed, in order both to evaluate its likelihood, in light of a set of experimental results described in the literature, and to predict precisely which are the sites of interaction between the two molecules. Our model is compatible with the experimentally determined characteristics of the complex. Some of the residues that form the predicted antigenic site of ferritin can be found in the amino acid sequence of peptides selected from a random peptide library because of their affinity for the ferritin monoclonal antibody. Furthermore, the structural difference between the antigenic site in human H-ferritin and the corresponding region in other species permits us to rationalize the inability of the antibody to recognize human L-ferritin and rat, chicken and mouse H-ferritin. Through the analysis of our model complex, we identify a number of other residues putatively involved in the interaction. This multidisciplinary approach shows that synergy between computational and experimental methods may bring further insight into the understanding of antibody-antigen recognition rules.