A synthetic decapeptide of primary structure, GQVLQGAIKG, and its analogues were discovered through a random screening exercise to bind to proteins, in particular to antibodies of the IgG class. The binding was studied, particularly with a view to developing a novel peptide-mediated separation system for antibodies and also for its potential as a targeting moiety in drug delivery.

A microwell plate assay technique was developed to screen a wide range of proteins for peptide-protein interaction. The decapeptide bound to polyclonal IgG from different animal sources, including goat IgG. The latter does not bind to protein A. The peptide also bound to a few other proteins. Further studies demonstrated that the decapeptide bound to the Fab and Fc fragments of IgG. Competition experiments showed that protein A and protein G binding to IgG was not inhibited by the decapeptide whether in its monomeric or multimeric form.

Sequential substitution of the peptide by alanine showed that the functional residues responsible for IgG binding activity are:​ Q², V³, L⁴, Q⁵ and I⁸. The periodicity of polar and non-polar residues was observed not to be a critical factor in the interaction of the sequence with IgG. Alanine substitution of residues with intrinsic propensities for P-sheet conformation, based on the Chou and Fasman parameters, resulted in the reduction or total loss of IgG binding activity. This suggests a P-sheet conformational preference may be involved in IgG binding. Self-competition studies indicated that solid-phases could contribute to the IgG binding activity of the peptide. Affinity chromatography studies showed that the decapeptide, when immobilised to support matrices, maintained its IgG recognition.

Attempts to estimate the binding affinity of peptide-IgG interactions in solution by fluorescence spectroscopy proved difficult, possibly as a result of the conjugated fluorophores affecting binding activity of the peptide. Kinetic studies on the interaction of the decapeptide with IgG using the surface plasmon resonance technique, estimated the equilibrium dissociation constant (K_D) for the interaction to be, 176 nM, in its monomeric form, and in the range 55 nM to 2.6 pM, in its tetrameric form.