The invention relates to a method of directing selection of biological therapeutic molecules to specific functional domains of the target biologic molecule. Selection is directed by the use of closely related molecules, where one is a decoy and the other contains the targeted domain or epitope. The invention is based on the use of physical data, which may be combined with derived data, to ascertain that the decoy and the target differ only in the specific functional domain or epitope where the binding will be directed.
