An atypical human immunoglobulin G with deletions in both heavy and light chains. Studies of the conformation and the in vitro recombination of the isolated subunits.

Abstract

Both the light and gamma (heavy) chains of IgG(Sac) contain extensive deletions in their variable regions. The deletion in the light chain is internal (residues 18–88), whereas the deletion in the heavy chain is amino-terminal (residues 1–102). The hypervariable region just preceding the beginning of the constant region in other heavy chains (residues 103–115) is amino-terminal in heavy chain(Sac). In 4 mM acetate, pH 5.4, heavy chain(Sac) is dimeric like normal gamma chains, whereas light chain(Sac) is monomeric. Isolated light and heavy chains of IgG(Sac) recombine in vitro with each other and also with the heavy and light chains from a typical human IgG1-K myeloma protein, but not in a fashion entirely typical of other human gamma and light chains. These studies support the concept that non-covalent forces between the variable regions of the light and heavy chains are important in the assembly of the immunoglobulin molecule; and in view of the weak interaction between the constant region of light chain and heavy chain observed previously, our data suggest that there are points of contact between the hypervariable region of the gamma chain (residues 103–115) and the variable region of the light chain.