Protein G, protein A and protein A-derived peptides inhibit the agitation induced aggregation of IgG

Controlling and preventing aggregation is critical to the development of safe and effective antibody drug products. The studies presented here test the hypothesis that protein A and protein G inhibit the agitation-induced aggregation of IgG. The hypothesis is motivated by the enhanced conformational stability of proteins upon ligand binding and the specific binding affinity of protein A and protein G to the Fc region of IgG. The aggregation of mixed human IgG from pooled human plasma was induced by agitation alone or in the presence of (i) protein A, (ii) protein G or (iii) a library of 24 peptides derived from the IgG-binding domain of protein A. Aggregation was assessed by UV spectroscopy, SDS-PAGE, high performance size-exclusion chromatography (HP-SEC), dynamic light scattering (DLS) and fluorescence spectroscopy. Additional information on IgG-ligand interactions was obtained using differential scanning fluorimetry (DSF) and competitive binding studies. The results demonstrate that protein A provides near-complete inhibition of agitation-induced aggregation, while protein G and two peptides from the peptide library show partial inhibition. The findings indicate that the IgG protein A-binding site is involved in the agitation-induced aggregation of IgG, and suggest a dominant role of colloidal interactions.