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Long-term metastable conformation of human Fcgamma subunit.

It was found that the human (hu) myeloma IgG1 Ser, its Fcgamma fragment and the chimeric mouse-human monoclonal antibody (chim-mAb), containing the constant part of hu-gamma1-chain, can exist in a long-term metastable conformational state. This state arises as a result of short incubation of IgG molecules and their Fcgamma fragments at pH<2.8 and the consequent rapid neutralisation to pH 7.0-8.0. At pH<2.8 the three-dimensional structure of C(gamma)2 domains is unfolded, but rapidly refolds after neutralisation. At the same time, non-covalent interactions between C(gamma)2 and C(gamma)3 domains are restored very slowly. A metastable state of IgG keeps 70% of complement-binding ability in comparison with the native state.