title: The C-terminal αI domain linker as a critical structural element in the conformational activation of αI integrins.
abstract: The activation of α/β heterodimeric integrins is the result of highly coordinated rearrangements within both subunits. The molecular interactions between the two subunits, however, remain to be characterized. In this study, we use the integrin α(L)β(2) to investigate the functional role of the C-linker polypeptide that connects the C-terminal end of the inserted (I) domain with the β-propeller domain on the α subunit and is located at the interface with the βI domain of the β chain. We demonstrate that shortening of the C-linker by eight or more amino acids results in constitutively active α(L)β(2) in which the αI domain is no longer responsive to the regulation by the βI domain. Despite this intersubunit uncoupling, both I domains remain individually sensitive to intrasubunit conformational changes induced by allosteric modulators. Interestingly, the length and not the sequence of the C-linker appears to be critical for its functionality in α/β intersubunit communication. Using two monoclonal antibodies (R7.1 and CBR LFA-1/1) we further demonstrate that shortening of the C-linker results in the gradual loss of combinational epitopes that require both the αI and β-propeller domains for full reactivity. Taken together, our findings highlight the role of the C-linker as a spring-like element that allows relaxation of the αI domain in the resting state and controlled tension of the αI domain during activation, exerted by the β chain.
authors.affiliation: Immune Disease Institute, Children's Hospital Boston and Department of Pathology, Harvard Medical School, Boston Massachusetts 02115; University Basel, PharmaCenter, Klingelbergstr. 50-70, 4056 Basel, Switzerland. Electronic address: gabriele.weitz-schmidt@unibas.ch.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Weitz-Schmidt
authors.affiliation: Immune Disease Institute, Children's Hospital Boston and Department of Pathology, Harvard Medical School, Boston Massachusetts 02115.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schürpf
authors.affiliation: Immune Disease Institute, Children's Hospital Boston and Department of Pathology, Harvard Medical School, Boston Massachusetts 02115. Electronic address: springer@idi.harvard.edu.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Springer
mesh_terms: D000495:Allosteric Site; D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D002448:Cell Adhesion; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D039423:Integrin alpha1 / Q000737:chemistry*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence / Q000379:methods; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D014162:Transfection
chemical_list: D000911:Antibodies, Monoclonal; D039423:Integrin alpha1; D016169:Lymphocyte Function-Associated Antigen-1