title: Activation-induced conformational changes in the I domain region of lymphocyte function-associated antigen 1.
abstract: Conformational changes in integrins are important for efficient ligand binding during activation. We proposed that the I domain of the integrin lymphocyte function-associated antigen 1 (LFA-1) could exist in both open and closed conformations and generated constitutively activated LFA-1 by locking the I domain in the open conformation. Here we provide structural and biochemical evidence to validate conformational change in the I domain of LFA-1 upon activation. Two monoclonal antibodies to alpha(L), HI111 and CBR LFA-1/1, bind wild-type LFA-1 well, but their binding is significantly reduced when LFA-1 is locked in the open conformation. Furthermore, this reduction in monoclonal antibody binding also occurs when LFA-1 is activated by divalent cations. HI111 maps to the top region of the I domain that is close to the putative ligand-binding site surrounding the MIDAS (metal ion-dependent adhesion site). The epitope of CBR LFA-1/1 is at the C-terminal segment of the I domain that links to the beta-propeller, and undergoes a large movement between the open and closed conformations. Our data demonstrate that these two regions undergo significant conformational changes during LFA-1 activation and that the I domain of activated LFA-1 adopts a similar tertiary structure as the predicted locked open form.
authors.affiliation: Department of Pathology, Center for Blood Research and Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Qing
authors.initials: Q
authors.lastname: Ma
authors.forename: Motomu
authors.initials: M
authors.lastname: Shimaoka
authors.forename: Chafen
authors.initials: C
authors.lastname: Lu
authors.forename: Hua
authors.initials: H
authors.lastname: Jing
authors.forename: Christopher V
authors.initials: CV
authors.lastname: Carman
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D002412:Cations; D002448:Cell Adhesion; D002460:Cell Line; D004229:Dithiothreitol / Q000494:pharmacology; D000939:Epitopes; D006801:Humans; D020014:K562 Cells; D007700:Kinetics; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020349:Surface Plasmon Resonance
chemical_list: D000911:Antibodies, Monoclonal; D002412:Cations; D000939:Epitopes; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D011993:Recombinant Fusion Proteins; D004229:Dithiothreitol