Primary structure of a small glycopeptide isolated from human glomerular basement membrane and carrying a major antigenic site.

Abstract

The glycopeptides containing either the disaccharide or the heteropolysaccharide chains were purified, after enzymatic digestion of glomerular basement‐membrane antigens, by gel filtration and ion‐exchange chromatography. Their antigenicity was investigated in seven patients with anti‐glomerular‐basement‐membrane antibody‐mediated glomerulonephritis, by the leukocyte migration test and radioimmunoassay.The leukocyte migration of the seven patients is inhibited in presence of membrane antigens with both types of oligosaccharide chains. The disaccharide‐containing glycopeptide inhibits the leukocyte migration of these patients using 10‐times less antigenic material; the heteropolysaccharide‐containing glycopeptide does not modify the leudkocyte migration of the same patients. Similarly, only the disaccharide‐containing glycopeptide decreases the binding of labelled membrane antigens with anti‐glomerular‐basement‐membrane antibodies, using the radioimmunoassay. This glycopeptide carries therefore the major antigenic determinants of humoral and cellular anti‐basement‐membrane auto‐immunization.The amino acid sequence of the glycopeptide is Hyl‐Gly‐Glu‐Asp‐Gly, the disaccharide prosthetic group being linked to the hydrolysine residue of the peptidic chain; its immunodominant antigenic site is formed by the Galp‐Hyl unit.