Basic amino-acid side chains regulate transmembrane integrin signalling

• Published in: Nature (London) 2012-01, Vol.481 (7380), p.209-213
• Main Authors: Kim, Chungho, Schmidt, Thomas, Cho, Eun-Gyung, Ye, Feng, Ulmer, Tobias S., Ginsberg, Mark H.
• Format: Article
• Language: English
• Subjects: 631/45/535; 631/80; 631/80/84/2342; Amino Acid Sequence; Amino acids; Animals; Biological and medical sciences; Cell Membrane - metabolism; Cell physiology; CHO Cells; Cricetinae; Directed Molecular Evolution; Experiments; Fundamental and applied biological sciences. Psychology; Genetic Complementation Test; Humanities and Social Sciences; Integrins; Integrins - chemistry; Integrins - genetics; Integrins - metabolism; letter; Lipids; Lysine - chemistry; Lysine - genetics; Lysine - metabolism; Membrane Lipids - metabolism; Membranes; Models, Molecular; Molecular and cellular biology; Molecular Sequence Data; multidisciplinary; Mutation; Mutation - genetics; Nuclear magnetic resonance spectroscopy; Nuclear Magnetic Resonance, Biomolecular; Physiological aspects; Pliability; Proline - chemistry; Proline - genetics; Proline - metabolism; Protein Binding; Protein Multimerization; Protein Stability; Protein Structure, Tertiary; Proteins; Science; Science (multidisciplinary); Signal Transduction; Topography
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature10697

Loss of a snorkelling residue in integrin β TMDs changes membrane embedding and affects transmembrane signalling, showing that snorkelling can have an important role in signal transduction Basic properties aid integrin signalling Cell adhesion receptors of the integrin family are composed of α and β type I transmembrane domains (TMDs). Interactions between the α and β TMDs play a crucial role in bidirectional signal transduction. Most integrin β subunits contain a positively charged Lys or Arg residue near the inner membrane boundary of the TMD. A structural and functional analysis using targeted mutation of these basic residues demonstrates that they are critical to the maintenance of TMD topography and α and β heterodimer association, thereby enabling precise regulation of transmembrane signalling. Side chains of Lys/Arg near transmembrane domain (TMD) 1 , 2 , 3 membrane–water interfaces can ‘snorkel’, placing their positive charge near negatively charged phospholipid head groups 4 , 5 , 6 ; however, snorkelling’s functional effects are obscure. Integrin β TMDs have such conserved basic amino acids. Here we use NMR spectroscopy 7 , 8 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 9 . 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.