Characterization of posttranslational modifications of human A33 antigen, a novel palmitoylated surface glycoprotein of human gastrointestinal epithelium

Biochem Biophys Res Commun. 1997 Jul 30;236(3):682-6. doi: 10.1006/bbrc.1997.6966.


Monoclonal antibody (mAb) A33 recognizes a differentiation antigen (A33) expressed in normal human gastrointestinal epithelium and in 95% of human colon cancers. Murine mAb A33 shows specific targeting of colon cancer in humans and a humanized A33 antibody is currently being evaluated in the clinic. The cDNA for the human A33 antigen has recently been cloned, and sequence comparison indicated that the A33 antigen is a novel human cell surface molecule of the immunoglobulin superfamily. Because mAb A33 recognizes a conformational epitope, only a partial characterization of the A33 antigen has been carried out to date. In this report we show that the A33 antigen is (I) N-glycosylated, containing approximately 8 K of N-linked carbohydrate and there is no evidence for O-glycosylation, sialylation or glycophosphatidylinositol, and (ii) S-acylated in vitro, incorporating [3H] palmitic acid linked through a hydroxylamine-sensitive thioester bond. The S-palmitoylation may be involved in regulating the internalization process initiated by binding of mAb A33 to cell surface A33 antigen.

MeSH terms

  • Acylation
  • Amino Acid Sequence
  • Animals
  • Antibodies, Monoclonal
  • Antigens, Neoplasm / metabolism*
  • Blotting, Western
  • Colonic Neoplasms / immunology
  • Digestive System / immunology*
  • Electrophoresis, Polyacrylamide Gel
  • Epithelium / immunology
  • Glycosylation
  • Humans
  • Immunosorbent Techniques
  • Membrane Glycoproteins / metabolism*
  • Mice
  • Palmitic Acid / metabolism*
  • Protein Processing, Post-Translational*


  • Antibodies, Monoclonal
  • Antigens, Neoplasm
  • GPA33 protein, human
  • Gpa33 protein, mouse
  • Membrane Glycoproteins
  • Palmitic Acid