Folding and function of I domain-deleted Mac-1 and lymphocyte function-associated antigen-1.
In those integrins that contain it, the I domain is a major ligand recognition site. The I domain is inserted between beta-sheets 2 and 3 of the predicted beta-propeller domain of the integrin alpha subunit. We deleted the I domain from the integrin alpha(M) and alpha(L) subunits to give I-less Mac-1 and lymphocyte function-associated antigen-1 (LFA-1), respectively. The I-less alpha(M) and alpha(L) subunits were expressed in association with the wild-type beta(2) subunit on the surface of transfected cells and bound to all the monoclonal antibodies mapped to the putative beta-propeller and C-terminal regions of the alpha(M) and alpha(L) subunits, suggesting that the folding of these domains is independent of the I domain. I-less Mac-1 bound to the ligands iC3b and factor X, but this binding was reduced compared with wild-type Mac-1. In contrast, I-less Mac-1 did not bind to fibrinogen or denatured bovine serum albumin. Binding to iC3b and factor X by I-less Mac-1 was inhibited by the function-blocking antibody CBRM1/32, which binds to the beta-propeller domain of the alpha(M) subunit. I-less LFA-1 did not bind its ligands intercellular adhesion molecule-1 and -3. Thus, the I domain is not essential for the folding, heterodimer formation, and surface expression of Mac-1 and LFA-1 and is required for binding to some ligands, but not others.
Yalamanchili
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Center for Blood Research and the Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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Oxvig
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Springer
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D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002460:Cell Line; D006801:Humans; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D016177:Macrophage-1 Antigen / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D017510:Protein Folding; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen