title: Gating function of isoleucine-116 in TM-3 (position III:16/3.40) for the activity state of the CC-chemokine receptor 5 (CCR5).
abstract: OBJECTIVE
  A conserved amino acid within a protein family indicates a significance of the residue. In the centre of transmembrane helix (TM)-5, position V:13/5.47, an aromatic amino acid is conserved among class A 7TM receptors. However, in 37% of chemokine receptors - a subgroup of 7TM receptors - it is a leucine indicating an altered function. Here, we describe the significance of this position and its possible interaction with TM-3 for CCR5 activity.
  
  
  METHODS
  The effects of [L203F]-CCR5 in TM-5 (position V:13/5.47), [I116A]-CCR5 in TM-3 (III:16/3.40) and [L203F;G286F]-CCR5 (V:13/5.47;VII:09/7.42) were determined in G-protein- and β-arrestin-coupled signalling. Computational modelling monitored changes in amino acid conformation.
  
  
  RESULTS
  [L203F]-CCR5 increased the basal level of G-protein coupling (20-70% of Emax ) and β-arrestin recruitment (50% of Emax ) with a threefold increase in agonist potency. In silico, [I116A]-CCR5 switched χ1-angle in [L203F]-CCR5. Furthermore, [I116A]-CCR5 was constitutively active to a similar degree as [L203F]-CCR5. Tyr(244) in TM-6 (VI:09/6.44) moved towards TM-5 in silico, consistent with its previously shown function for CCR5 activation. On [L203F;G286F]-CCR5 the antagonist aplaviroc was converted to a superagonist.
  
  
  CONCLUSIONS
  The results imply that an aromatic amino acid in the centre of TM-5 controls the level of receptor activity. Furthermore, Ile(116) acts as a gate for the movement of Tyr(244) towards TM-5 in the active state, a mechanism proposed previously for the β2 -adrenoceptor. The results provide an understanding of chemokine receptor function and thereby information for the development of biased and non-biased antagonists and inverse agonists.
authors: Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, The Panum Institute, University of Copenhagen, Copenhagen, Denmark.
authors: A
authors: A
authors: Steen
authors: A H
authors: AH
authors: Sparre-Ulrich
authors: S
authors: S
authors: Thiele
authors: D
authors: D
authors: Guo
authors: T M
authors: TM
authors: Frimurer
authors: M M
authors: MM
authors: Rosenkilde
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D015640:Ion Channel Gating; D007532:Isoleucine / Q000502:physiology*; D008969:Molecular Sequence Data; D019713:Receptors, CCR5 / Q000737:chemistry / Q000502:physiology*; D017386:Sequence Homology, Amino Acid
chemical_list: D019713:Receptors, CCR5; D007532:Isoleucine
keywords: 7TM; CCR5; GPCR; US28; arrestin; biased signalling; chemokines; computer modelling; constitutive activity; superagonist