Antigenicity of metallothionein.

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Abstract
The antigenic determinants of vertebrate metallothionein were determined by a competitive-binding double-antibody radioimmunoassay to consist of 2 immunologically dominant regions in the NH2-terminal domain (residues 1-29). The COOH-terminal domain (residues 30-61) exhibited trivial immunoreactivity in competitive binding assays. The tryptic peptide encompassing residues 1-25 of the molecule competed with 125I-labeled metallothionein as effectively as the native protein. The crossreactivity was unaffected whether the protein was native or denatured. The antigenicity is thus independent of the degree of folding of the protein and, although all antigenic sites depend to some degree on conformation or topography, this favors a sequential (or continuous) rather than a discontinuous nature of the determinants. The 2 regions in metallothionein that appear to be important in the interaction of the molecule with the antisera include the NH2-terminal acetylated methionine and the cluster of lysines in the sequence from residues 20-25. These regions are homologous in the various vertebrate metallothioneins known to crossreact with rabbit anti-rat metallothionein antiserum. The induction of rabbits of antiserum to rat metallothionein is apparently an autoimmune phenomenon. The 2 cluster model of metallothionein was supported, and predictions of sites of antigenicity based on regions of high hydrophilicity were corroborated.