Dyax Corp. wanted to understand how their antibody (DX-2930) was inhibiting a protease involved in hereditary angioedema (HAE).
EXPERIENCE / INSIGHT:
Beryllium generated recombinant human plasma kallikrein (pKal) for assays and crystallization using baculovirus infected insect cells with secreted expression and native refolding. Complex formation with the Dyax provided Fab of DX-2930 was used to determine a proper stoichiometric ratio, essential for success in crystallography. To understand the interaction between DX-2930 and pKal with atomic resolution, we crystallized the Fab portion of DX-2930 both alone and in a complex with a deglycosylated variant of the human pKal catalytic domain.
Results clearly showed the molecular details of the epitope/paratope interactions, thus providing a biological rational to how the antibody is functioning. In the Fab alone structure, the CDR loops are disordered, thus suggesting the antibody-antigen interaction is not preformed, thus the interaction between the two is an induced fit. DX-2930 functions by specifically blocking the active site of pKal, thus acting similar to the Serpin C1 inhibitor that is deficient in individuals with hereditary angioedema.