title: Basic amino-acid side chains regulate transmembrane integrin signalling.
abstract: Side chains of Lys/Arg near transmembrane domain (TMD) membrane-water interfaces can 'snorkel', placing their positive charge near negatively charged phospholipid head groups; however, snorkelling's functional effects are obscure. Integrin β TMDs have such conserved basic amino acids. Here we use NMR spectroscopy to show that integrin β(3)(Lys 716) helps determine β(3) TMD topography. The α(ΙΙb)β(3) TMD structure indicates that precise β(3) TMD crossing angles enable the assembly of outer and inner membrane 'clasps' that hold the αβ TMD together to limit transmembrane signalling. Mutation of β(3)(Lys 716) caused dissociation of α(ΙΙb)β(3) TMDs and integrin activation. To confirm that altered topography of β(3)(Lys 716) mutants activated α(ΙΙb)β(3), we used directed evolution of β(3)(K716A) to identify substitutions restoring default state. Introduction of Pro(711) at the midpoint of β(3) TMD (A711P) increased α(ΙΙb)β(3) TMD association and inactivated integrin α(ΙΙb)β(3)(A711P,K716A). β(3)(Pro 711) introduced a TMD kink of 30 ± 1° precisely at the border of the outer and inner membrane clasps, thereby decoupling the tilt between these segments. Thus, widely occurring snorkelling residues in TMDs can help maintain TMD topography and membrane-embedding, thereby regulating transmembrane signalling.
authors.affiliation: Department of Medicine, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: Chungho
authors.initials: C
authors.lastname: Kim
authors.forename: Thomas
authors.initials: T
authors.lastname: Schmidt
authors.forename: Eun-Gyung
authors.initials: EG
authors.lastname: Cho
authors.forename: Feng
authors.initials: F
authors.lastname: Ye
authors.forename: Tobias S
authors.initials: TS
authors.lastname: Ulmer
authors.forename: Mark H
authors.initials: MH
authors.lastname: Ginsberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D019020:Directed Molecular Evolution; D005816:Genetic Complementation Test; D016023:Integrins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008239:Lysine / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008563:Membrane Lipids / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D018583:Pliability; D011392:Proline / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D055550:Protein Stability; D017434:Protein Structure, Tertiary; D015398:Signal Transduction
chemical_list: D016023:Integrins; D008563:Membrane Lipids; D011392:Proline; D008239:Lysine