Mouse Ig coded by V(H) families S107 or J606 bind to protein A

Twenty-five monoclonal mouse Ig (5 IgA, 7 IgM, and 13 IgG1) were tested for binding to staphylococcal protein A. They were allowed to attach to protein A Sepharose column at pH 8.0 and were then eluted with a pH gradient from ~ 7.5 to 3.0. Five of them (IgM or IgA) did not bind. Ten came off with pH ~ 6. They were all IgG1, and were probably bound (weakly) via the Fc portion. The remaining 10 (3 IgA, 4 IgM, and 3 IgG1) were more firmly bound; they came off with pH-values ranging from 5.0 to 3.5. They all expressed V(H) genes of families J606 or S107, whereas all the 15 Ig that were not firmly bound expressed V(H) genes of six other families. The V(L) domains seem to be unimportant for protein A binding inasmuch as a firmly binding and a weakly binding IgG1 antibody share identical V(κ) domains. V(H) sequences of protein A-binding and nonbinding Ig were compared. No likely peptide sequences were found that might make the ligand for protein A.