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The Presence of Arginyl Residues and Carboxylate Groups in the Phosphorylcholine-Binding Site of Mouse Myeloma Protein, HOPC 8¹

From the Department of Immunology Research, Roswell Park Memorial Institute² 666 Elm Street, Buffalo, New York 14203

Abstract

The participation of certain amino acid residues in the phosphorylcholine-binding sites of the mouse myeloma protein, HOPC 8, has been investigated by chemical modification procedures. Glyoxalation of two-thirds of the arginyl residues of HOPC 8, in the absence of protecting ligand, resulted in the complete loss of binding activity; glyoxalation in the presence of phosphorylcholine resulted in retention of about 50% of the sites. Maleylation of all free amino groups of HOPC 8 caused a minor loss (20%) of binding activity whether or not ligand was present during the modification. Esterification of approximately one-quarter of the carboxylate groups of HOPC 8 resulted in a significant loss of binding sites and this loss could be partially prevented by the presence of ligand.

These results are interpreted as indicating the presence of arginyl and glutamyl or aspartyl residues as contact amino acids in the binding site of HOPC 8, providing complementary positive and negative charges for binding, respectively, the negatively charged phosphoryl moiety and the positively charged choline moiety of the ligand. Lysyl residues are probably not involved directly in the specific site-ligand interaction.

Footnotes

¹ This work was supported in part by United States Public Health Service Grant CA-11656.

² A unit of the New York State Department of Health.