title: NMR characterization of the conformational fluctuations of the human lymphocyte function-associated antigen-1 I-domain.
abstract: Lymphocyte function-associated antigen-1 (LFA-1) is an integrin protein that transmits information across the plasma membrane through the so-called inside-out and outside-in signaling mechanisms. To investigate these mechanisms, we carried out an NMR analysis of the dynamics of the LFA-1 I-domain, which has enabled us to characterize the motions of this domain on a broad range of timescales. We studied first the internal motions on the nanosecond timescale by spin relaxation measurements and model-free analysis. We then extended this analysis to the millisecond timescale motions by measuring (15) N-(1) H residual dipolar couplings of the backbone amide groups. We analyzed these results in the context of the three major conformational states of the I-domain using their corresponding X-ray crystallographic structures. Our results highlight the importance of the low-frequency motions of the LFA-1 I-domain in the inactive apo-state. We found in particular that α-helix 7 is in a position in the apo-closed state that cannot be fully described by any of the existing X-ray structures, as it appears to be in dynamic exchange between different conformations. This type of motion seems to represent an inherent property of the LFA-1 I-domain and might be relevant for controlling the access to the allosteric binding pocket, as well as for the downward displacement of α-helix 7 that is required for the activation of LFA-1.
authors.affiliation: Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom; Biozentrum, University of Basel, Basel, CH-4056, Switzerland.
authors.forename: Hoi Tik Alvin
authors.initials: HT
authors.lastname: Leung
authors.forename: Predrag
authors.initials: P
authors.lastname: Kukic
authors.forename: Carlo
authors.initials: C
authors.lastname: Camilloni
authors.forename: Francesco
authors.initials: F
authors.lastname: Bemporad
authors.forename: Alfonso
authors.initials: A
authors.lastname: De Simone
authors.forename: Francesco A
authors.initials: FA
authors.lastname: Aprile
authors.forename: Janet R
authors.initials: JR
authors.lastname: Kumita
authors.forename: Michele
authors.initials: M
authors.lastname: Vendruscolo
mesh_terms: D006801:Humans; D016169:Lymphocyte Function-Associated Antigen-1 / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation
chemical_list: D016169:Lymphocyte Function-Associated Antigen-1
keywords: NMR spectroscopy; allostery; protein dynamics; signaling mechanism