Post-translational protein modification and expression of ankyrin-binding site(s) in GP85 (Pgp-1/CD44) and its biosynthetic precursors during T-lymphoma membrane biosynthesis

V. B. Lokeshwar, L. Y.W. Bourguignon

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98 Scopus citations

Abstract

In this study, we have investigated the biosynthesis and processing of GP85 (Pgp-1/CD44), a lymphoma transmembrane glycoprotein known to contain ankyrin-binding site(s). Using a standard pulse-chase protocol, we have detected a 52-kDa polypeptide precursor (p52) within the first 5 min of pulse labeling which contains a high mannose-type N-linked oligosaccharide chains. The conversion of p52 to GP85 requires further glycosylation (both complex type N-linked and O-linked) which takes place in the Golgi complex within 10-20 min after p52 is synthesized. GP85 is then incorporated into the plasma membrane where its turnover rate is relatively slow, a t1/2 of approximately 8 h. Following tunicamycin treatment, we have detected two other precursor proteins: p42 which is unglycosylated and p58 which is O-glycosylated. p42 appears to be an immediate precursor of p52 because p52 is converted to p42 upon deglycosylation. Therefore, the biosynthesis of GP85 appears to occur in the following sequence: p42 → p52 → GP85. Further analysis reveals that all of the GP85 precursors (i.e. p42, p52, and p58) contain ankyrin-binding site(s). Chemical composition analysis of GP85 indicates that this molecule contains approximately 3 N-linked and 4-5 O-linked oligosaccharide chains. Although neither N-glycosylation nor O-glycosylation appears to play an important role in the formation of ankyrin-binding site(s), O-glycosylation (and to a lesser extent N-glycosylation) of GP85 is required for T-lymphoma cell surface interaction with both collagen and hyaluronic acid. These findings suggest that GP85 (Pgp-1/ CD44) and its biosynthetic precursors play a pivotal role in regulating adhesion functions such as lymphocyte homing and binding to the extracellular matrix.

Original languageEnglish (US)
Pages (from-to)17983-17989
Number of pages7
JournalJournal of Biological Chemistry
Volume266
Issue number27
StatePublished - Nov 8 1991

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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