title: Serine phosphorylation of syndecan-2 proteoglycan cytoplasmic domain.
abstract: Protein kinase C (PKC) is involved in cell-matrix and cell-cell adhesion, and the cytoplasmic domain of syndecan-2 contains two serines (residues 197 and 198) which lie in a consensus sequence for phosphorylation by PKC. Other serine and threonine residues are present but not in a consensus sequence. We investigated phosphorylation of syndecan-2 cytoplasmic domain by PKC, using purified GST-syndecan-2 fusion proteins and synthetic peptides corresponding to regions of the cytoplasmic domain. A synthetic peptide encompassing the entire cytoplasmic domain of syndecan-2 was phosphorylated by PKC with high affinity. Peptide mapping and substitution studies showed that both serines were phosphoacceptors, but each had slightly different affinity, with that of serine-197 being higher than serine-198. The efficiency of phosphorylation was concentration-dependent. At low concentrations, the cytoplasmic domain peptides were monomeric, with 2 mol/mol serine phosphorylation. At higher concentrations, however, the peptides formed dimers, with only 0.5 mol/mol phosphorylation. Concentration-dependent dimerization was not altered by phosphorylation. Phosphorylation is, therefore, dependent on the conformation of syndecan-2 cytoplasmic domain, but does not affect its oligomeric status.
authors.affiliation: Department of Cell Biology, and Cell Adhesion and Matrix Research Center, University of Alabama at Birmingham, 35294, USA.
authors.forename: E S
authors.initials: ES
authors.lastname: Oh
authors.forename: J R
authors.initials: JR
authors.lastname: Couchman
authors.forename: A
authors.initials: A
authors.lastname: Woods
mesh_terms: D000595:Amino Acid Sequence; D015153:Blotting, Western; D002850:Chromatography, Gel; D002855:Chromatography, Thin Layer; D003593:Cytoplasm / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics; D005982:Glutathione Transferase / Q000235:genetics; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D010748:Phosphopeptides / Q000032:analysis; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D011509:Proteoglycans / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D053669:Syndecan-2
chemical_list: D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D010710:Phosphates; D010748:Phosphopeptides; D011509:Proteoglycans; D011993:Recombinant Fusion Proteins; D053669:Syndecan-2; D010768:Phosphoserine; D005982:Glutathione Transferase; D011493:Protein Kinase C