The role of the I domain in ligand binding of the human integrin alpha 1 beta 1.
We report here the analysis of potential ligand binding domains within the human integrin alpha 1 subunit, a known collagen/laminin receptor. This integrin is effectively blocked by the mouse monoclonal antibody 1B3.1. A truncated version of the alpha 1 subunit lacking the NH2-terminal half of the extracellular domain is not recognized by monoclonal antibody 1B3.1. Furthermore, we have isolated a cDNA containing the I domain from chicken alpha 1 bearing significant homology to the human and rat alpha 1 sequences. Replacing the human I domain with its chicken counterpart led to the surface expression of a functional heterodimer with endogenous mouse beta 1 on NIH 3T3 cells. However, 1B3.1 does not bind to the chicken/human chimera, demonstrating that the human alpha 1 I domain is required for epitope recognition. Mutation of Asp253 within the I domain to alanine resulted in surface expression of an alpha beta heterodimer recognized by 1B3.1 but with markedly reduced binding to collagen IV or laminin. Since a previously reported mutation of a homologous Asp in the Mac-1 I domain has similar consequences, these results suggest a central role for the I domain in ligand recognition for all integrin alpha subunits containing this domain.
Kern
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Department of Pathology, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Briesewitz
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Bank
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Marcantonio
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D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001483:Base Sequence; D001665:Binding Sites; D002448:Cell Adhesion; D002645:Chickens; D002846:Chromatography, Affinity; D017931:DNA Primers; D000939:Epitopes / Q000032:analysis; D005895:Gizzard, Avian; D006801:Humans; D039222:Integrin alpha1beta1; D016023:Integrins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000378:metabolism; D011061:Poly A / Q000096:biosynthesis / Q000378:metabolism; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D000911:Antibodies, Monoclonal; D017931:DNA Primers; D000939:Epitopes; D039222:Integrin alpha1beta1; D016023:Integrins; D008024:Ligands; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D011061:Poly A