It is an immunoglobulin G-kappa (IgGκ) consisting of human constant regions and murine complementarity-determining regions grafted onto human framework light and heavy chain variable regions.

The high affinity of protein G for the Fab portion of IgG poses a particular challenge in molecular recognition, given the variability of heavy chain subclass, light chain type and complementarity-determining regions.

Using this method, Wilchek collaborated with a team who proved that the binding site of antibodies lies in the Fv portion of the molecule and involves three hypervariable sites, today called the complementarity-determining regions (CDRs).

They discovered the "canonical-structure model" for the conformation of the complementarity-determining regions of antibodies, and they applied this model to the analysis of antibody-germ-line genes, including the prediction of the structure of the corresponding proteins.