Light Scattering Study of the Antibody-Poly(methacrylic acid) and Antibody-Poly(acrylic acid) Conjugates in Aqueous Solutions

The effect of the conformational state of the polymer coil on the properties of protein-polymer conjugates has been studied for the conjugates of antibody (monoclonal antibody from 6C5 clone against inactivated rabbit muscle glyceraldehyde-3-phosphate dehydrogenase; Ab) with poly(methacrylic acid) (PMAA) or poly-(acrylic acid) (PAA). The pH-dependencies of molecular properties and structural parameters of aqueous solutions (radius of gyration, intensity of scattered light, hydrodynamic diameter, and polydisperisty index) of Ab, PMAA, and PAA, have been studied using static and dynamic light scattering techniques. While free Ab aggregates in solution and precipitates at its isoelectric point, the covalent attachment of a charged polymer to Ab prevents its association and shifts the precipitation point towards more acidic values (from pH 5.95 for Ab to pH ∼ 4.8 for Ab- PMAA). The predominant role of the conformational status of the polymer in the process of conjugate precipitation has been considered. Contrary to the precipitation of Ab-PMAA, the formation of stable colloidal particles was suggested for Ab-PAA at pH < 4.8. In the conjugates, polymer chains surround the protein globule in an extremely compact manner while Ab significantly affects the polymer conformation. The essentially larger hydrodynamic radii of conjugates, when compared with their radii of gyration, confirm the strong interaction of conjugates with solvent molecules.