title: 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.
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 in equilibrium to p52 in equilibrium to 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.
authors.affiliation: Department of Cell Biology and Anatomy, School of Medicine, University of Miami, Florida 33101.
authors.forename: V B
authors.initials: VB
authors.lastname: Lokeshwar
authors.forename: L Y
authors.initials: LY
authors.lastname: Bourguignon
mesh_terms: D000818:Animals; D017487:Ankyrins; D001665:Binding Sites; D001798:Blood Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006031:Glycosylation; D016399:Lymphoma, T-Cell / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008985:Monensin / Q000494:pharmacology; D011233:Precipitin Tests; D011498:Protein Precursors / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D016201:Receptors, Lymphocyte Homing / Q000096:biosynthesis / Q000378:metabolism*; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D017487:Ankyrins; D001798:Blood Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011498:Protein Precursors; D016201:Receptors, Lymphocyte Homing; D014415:Tunicamycin; D008985:Monensin