The effect of dodecyl sulfate on immunoglobulin hapten binding

Multistep denaturation and hierarchy of disulfide bond cleavage of a monoclonal antibody

A humanized, monoclonal antibody of the IgG4 class was treated with SDS at room temperature. Analysis using SDS-PAGE revealed the progressive formation of a series of denaturation intermediates, of increasing apparent molecular weights. The detectable species migrated with apparent molecular weights of 137, 152, 162, 182, 196, and 210 kDa. Antibody not incubated in SDS had an apparent molecular weight of 137 kDa, while boiling in SDS provoked the immediate conversion of all antibody to the slowest migrating form (210 kDa). A study designed to test if all rungs of the ladder were equally cleavable by mild treatment with mercaptoethanol revealed small amounts of a novel form, and conditions were devised to generate large amounts of this novel form. The novel form, before full denaturation, migrated at the position of unheated, intact antibody (137 kDa), while full denaturation in SDS converted the novel form to a species migrating at about 190 kDa. The novel form, before full denaturation, was identified as HHL ***L, where the asterisks indicate noncovalent binding of one light chain to HHL. This noncovalent complex remains intact during SDS-PAGE. The novel form, after full denaturation, was identified as HHL. This study, with earlier studies, reveals that different pathways of reductive cleavage are taken by different antibodies, and that the most sensitive disulfide bond is different for different antibodies. Our results on antibody denaturation serve as a warning to those who use two-dimensional gels for the analysis of antibodies.

Immunological comparison of major outer membrane proteins from different strains of Escherichia coli

Rabbits were immunized with either the native trimer or the denatured monomer of OmpF porin of Escherichia coli. The specificity of the two antisera was checked by two different techniques. In liquid immunorecognition assays, the antisera detected the presence of common antigenic determinants at the surface of the monomer and trimer forms. A high response was observed between the two antisera and the native form of OmpF. Although cross-reactivity between the antiserum directed against the OmpF monomer and a denatured form of PhoE was obtained, this denatured porin was weakly recognized by the antiserum specific to the native protein. In immunoblotting experiments, though antiserum directed against the native porin detected the two forms of OmpF, antiserum specific to the monomer recognized only the denatured protein. These two antisera were used to check the immunological relationships of E. coli strains isolated from various contaminated waters. Proteins from several wild strains were compared to the immunoblotting patterns of E. coli reference strains. Porins from the majority of these wild strains were immunorelated to porins of the ML30 strain. In two strains, porins were related to the OmpC/OmpF of the K12 strain, and one strain contained a porin identical to the OmpF of the B strain. Thus, an immunological approach using polyclonal antibodies directed against a major outer membrane protein appears to be fruitful for an accurate classification of various E. coli strains. Moreover, the ecological habitat of a strain can also be investigated by this analysis.