title: The role of Ca2+ binding in the self-aggregation of laminin-nidogen complexes.
abstract: Laminin-nidogen complexes were found to aggregate in the presence of divalent cations in a manner dependent on ion concentration. This effect shows a selectivity for Ca2+, as half-maximal aggregation is achieved already at about 10 microM Ca2+, while Mg2+ induces aggregation at 10-fold higher ion concentrations and always to a lesser extent. When binding of Ca2+ to laminin-nidogen complexes was measured by equilibrium dialysis, a total of about 16 binding sites with dissociation constants in the range of 5-300 microM could be identified. At 50 microM Ca2+, where the aggregation is maximal, only two to three Ca2+ ions are bound to laminin-nidogen complexes, indicating that the aggregation reaction is induced by the binding of Ca2+ to a small number of sites and possibly to a single distinct site. Analysis of Ca2+ binding to various proteolytic fragments of laminin allowed the tentative localization of a high affinity binding site to a large fragment comprising two of the short arms connected by the central part of the laminin molecule.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D007797:Laminin / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D008970:Molecular Weight; D009391:Nephelometry and Turbidimetry; D011487:Protein Conformation; D012513:Sarcoma, Experimental / Q000378:metabolism
chemical_list: D007797:Laminin; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C029967:nidogen; D008274:Magnesium; D002118:Calcium