Intermolecular interactions and conformation of antibody

Intermolecular interactions and conformation in dimer species of Palivizumab, a monoclonal antibody (IgG1), were investigated to elucidate the physical and chemical properties of the dimerized antibody. Palivizumab solu-tion contains 1 % dimer and 99 % monomer. The dimer species was isolated by size-exclusion chromatog-raphy and analysed by a number of methods including analytical ultracentrifugation-sedimantetion velocity (AUC-SV). AUC-SV in the presence of sodium dodecyl sulphate indicated that approximately half of the dimer fraction was non-covalently associated, whereas the other half was dimerized by covalent bond. Disulphide bond and dityrosine formation were likely to be involved in the covalent dimerization. Limited proteoly-sis of the isolated dimer by Lys-C and mass spectrom-etry for the resultant products indicated that the dimer species were formed by FabFc or FabFab interactions, whereas FcFc interactions were not found. It is thus likely that the dimerization occurs mainly via the Fab region. With regard to the conformation of the dimer species, the secondary and tertiary structures were shown to be almost identical to those of the monomer. Furthermore, the thermal stability turned out also to be very similar between the dimer and monomer