Binding and functional properties of concanavalin A and its derivatives. II. A proteolytic product with saccharide-binding activity.
Limited digestion of the intact subunit of concanavalin A (Mr = 26,000) with trypsin followed by affinity chromatography on Sephadex G-100 has yielded a highly purified product designated here as Tn-Con A. Chemical studies have shown that Tn-Con A is composed of several components: a large fragment (Tn I, Mr = 19,000) spanning residues 1 to 172, and lower molecular weight polypeptides that are noncovalently associated with Tn I to form the active molecule. The molecular weight of Tn-Con A at pH 7 was 90,000, suggesting that, like native concanavalin A, it was a tetramer at physiological pH. Equilibrium dialysis experiments showed that Tn-Con A bound 1 molecule of alpha-methyl-D-glucoside/22,000 g atoms of protein and therefore that four saccharides are bound by the tetrameric molecule. Tn-Con A and native concanavalin A competed for the same receptors on the lymphocyte surface. Moreover, Tn-Con A was mitogenic for both mouse and human lymphocytes with dose-response curves similar to those of the native lectin. All of these results indicate that tryptic hydrolysis of concanavalin A produces a fragmented molecule retaining the saccharide-binding, subunit association, and mitogenic capacity of the native protein.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001681:Biological Assay; D003208:Concanavalin A / Q000031:analogs & derivatives*; D008213:Lymphocyte Activation; D008757:Methylglucosides; D008759:Methylglycosides; D051379:Mice; D008970:Molecular Weight; D010434:Pepsin A; D010446:Peptide Fragments; D011485:Protein Binding; D014357:Trypsin
D000596:Amino Acids; D008757:Methylglucosides; D008759:Methylglycosides; D010446:Peptide Fragments; D003208:Concanavalin A; D014357:Trypsin; D010434:Pepsin A