Manganese Ion Elicits a Binding Activity of Placenta Vitronectin Receptor to Fibronectin Cell-Binding Domain

Abstract

Some members of the integrin family recognize the RGD sequence which is common to cell adhesive proteins in a divalent cation-dependent manner. In the presence of Ca²⁺ and Mg²⁺, the fibronectin receptor of placenta recognizes the RGD sequence of fibronectin, but not that of vitronectin, while the vitronectin receptor of placenta recognizes the RGD sequence of vitronectin, but not that of fibronectin, although both receptors recognize the same RGD sequence. We have found by performing an enzyme-linked immunosorbent assay (ELISA) using receptor-specific monoclonal antibodies and by electrophoretic analysis that in the presence of Mn²⁺ a vitronectin receptor of placenta binds to an affinity column coupled with the cell-binding domain of fibronectin. By replacing divalent cations from Mn²⁺ to Ca²⁺ and Mg²⁺, the vitronectin receptor was completely eluted from the column. When the synthetic peptides GRGDSP and GRGESP were applied to the column as competitors, the Mn²⁺-dependent binding was inhibited by both peptides. These results suggest that Mn²⁺ elicits a binding activity of the placenta vitronectin receptor to the RGD site of fibronectin. The modulation of ligand specificity by Mn²⁺ will provide an important clue in the elucidation of the cause of individual ligand specificity of RGD-recognizing integrins.