Binding of the alpha 2 integrin I domain to extracellular matrix ligands: structural and mechanistic differences between collagen and laminin binding.
The alpha 2 beta 1 integrin functions as a cell surface receptor for collagen on some cells and as both a collagen and laminin receptor on a more restricted subset of cell types including endothelial and epithelial cells. The alpha 2 integrin subunit I domain binds collagen in a divalent cation-dependent manner. In contrast, I domain binding to laminin occurs via both divalent cation-dependent and -independent mechanisms. Saturable binding was observed in the presence of either Mn2+ or EDTA, although the extent of binding in Mn2+ was twice that observed in EDTA. Half-maximal binding occurred at about 22 nM I domain in either case. Whereas laminin binding was significantly enhanced by Mn2+, with half-maximal binding occurring at 1.9 mM Mn2+, Mg2+ was much less effective. Deletion of the N-terminal 35 residues of the I domain, including the DXSXS portion of the MIDAS motif, caused a significant diminution of laminin binding activity. Laminin binding by the I domain was significantly inhibited by the alpha 2 beta 1 function-blocking antibody 6F1 in the presence of either EDTA or Mn2+. The non-function-blocking antibody 12F1 had no effect. In contrast to the binding of the alpha 2 integrin I domain to collagen, the laminin binding activity of the I domain was not enhanced by the addition of the first EF hand motif of the integrin.
Department of Pathology, Washington University School of Medicine, St. Louis, MO 63110, USA.
S K
SK
Dickeson
J J
JJ
Walsh
S A
SA
Santoro
D000911:Antibodies, Monoclonal; D015703:Antigens, CD / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D003001:Cloning, Molecular; D003094:Collagen / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism*; D006801:Humans; D039421:Integrin alpha2; D007797:Laminin / Q000276:immunology / Q000378:metabolism*; D008024:Ligands; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D016296:Mutagenesis / Q000502:physiology; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D017434:Protein Structure, Tertiary
D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D002413:Cations, Divalent; D002614:Chelating Agents; D039421:Integrin alpha2; D007797:Laminin; D008024:Ligands; D008345:Manganese; D003094:Collagen; D004492:Edetic Acid; D008274:Magnesium