title: The heparin-binding activity of secreted modular calcium-binding protein 1 (SMOC-1) modulates its cell adhesion properties.
abstract: Secreted modular calcium-binding proteins 1 and 2 (SMOC-1 and SMOC-1) are extracellular calcium- binding proteins belonging to the BM-40 family of proteins. In this work we have identified a highly basic region in the extracellular calcium-binding (EC) domain of the SMOC-1 similar to other known glycosaminoglycan-binding motifs. Size-exclusion chromatography shows that full length SMOC-1 as well as its C-terminal EC domain alone bind heparin and heparan sulfate, but not the related chondroitin sulfate or dermatan sulfate glycosaminoglycans. Intrinsic tryptophan fluorescence measurements were used to quantify the binding of heparin to full length SMOC-1 and the EC domain alone. The calculated equilibrium dissociation constants were in the lower micromolar range. The binding site consists of two antiparallel alpha helices and mutagenesis experiments have shown that heparin-binding residues in both helices must be replaced in order to abolish heparin binding. Furthermore, we show that the SMOC-1 EC domain, like the SMOC-2 EC domain, supports the adhesion of epithelial HaCaT cells. Heparin-binding impaired mutants failed to support S1EC-mediated cell adhesion and together with the observation that S1EC in complex with soluble heparin attenuated cell adhesion we conclude that a functional and accessible S1EC heparin-binding site mediates adhesion of epithelial cells to SMOC-1.
authors: Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Ljubljana, Slovenia.
authors: Marina
authors: M
authors: Klemenčič
authors: Marko
authors: M
authors: Novinec
authors: Silke
authors: S
authors: Maier
authors: Ursula
authors: U
authors: Hartmann
authors: Brigita
authors: B
authors: Lenarčič
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002448:Cell Adhesion / Q000502:physiology; D006493:Heparin / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D008969:Molecular Sequence Data; D009154:Mutation; D015676:Osteonectin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D011509:Proteoglycans / Q000378:metabolism; D016415:Sequence Alignment; D014364:Tryptophan / Q000737:chemistry
chemical_list: D015676:Osteonectin; D011509:Proteoglycans; C524549:SMOC-1 protein, mouse; D014364:Tryptophan; D006493:Heparin