The TXP motif in the second transmembrane helix of CCR5. A structural determinant of chemokine-induced activation.
CCR5 is a G-protein-coupled receptor activated by the chemokines RANTES (regulated on activation normal T cell expressed and secreted), macrophage inflammatory protein 1alpha and 1beta, and monocyte chemotactic protein 2 and is the main co-receptor for the macrophage-tropic human immunodeficiency virus strains. We have identified a sequence motif (TXP) in the second transmembrane helix of chemokine receptors and investigated its role by theoretical and experimental approaches. Molecular dynamics simulations of model alpha-helices in a nonpolar environment were used to show that a TXP motif strongly bends these helices, due to the coordinated action of the proline, which kinks the helix, and of the threonine, which further accentuates this structural deformation. Site-directed mutagenesis of the corresponding Pro and Thr residues in CCR5 allowed us to probe the consequences of these structural findings in the context of the whole receptor. The P84A mutation leads to a decreased binding affinity for chemokines and nearly abolishes the functional response of the receptor. In contrast, mutation of Thr-82(2.56) into Val, Ala, Cys, or Ser does not affect chemokine binding. However, the functional response was found to depend strongly on the nature of the substituted side chain. The rank order of impairment of receptor activation is P84A > T82V > T82A > T82C > T82S. This ranking of impairment parallels the bending of the alpha-helix observed in the molecular simulation study.
Institut de Recherche Interdisciplinaire en Biologie Humaine et Nucléaire, Université Libre de Bruxelles, Campus Erasme, 808 route de Lennik, B-1070 Bruxelles, Belgium.
C
C
Govaerts
C
C
Blanpain
X
X
Deupi
S
S
Ballet
J A
JA
Ballesteros
S J
SJ
Wodak
G
G
Vassart
L
L
Pardo
M
M
Parmentier
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells; D002417:Cattle; D054407:Chemokine CCL4; D018946:Chemokine CCL5 / Q000493:pharmacokinetics / Q000494:pharmacology; D054412:Chemokine CCL8; D018925:Chemokines / Q000494:pharmacology*; D006224:Cricetinae; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D019402:Macrophage Inflammatory Proteins / Q000494:pharmacology; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018945:Monocyte Chemoattractant Proteins / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D019713:Receptors, CCR5 / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology*; D019707:Receptors, Chemokine / Q000737:chemistry; D015728:Receptors, HIV / Q000737:chemistry / Q000187:drug effects / Q000502:physiology; D011994:Recombinant Proteins / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D012243:Rhodopsin / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection
C515453:CCL8 protein, human; C515454:Ccl8 protein, mouse; D054407:Chemokine CCL4; D018946:Chemokine CCL5; D054412:Chemokine CCL8; D018925:Chemokines; D019402:Macrophage Inflammatory Proteins; D018945:Monocyte Chemoattractant Proteins; D019713:Receptors, CCR5; D019707:Receptors, Chemokine; D015728:Receptors, HIV; D011994:Recombinant Proteins; D012243:Rhodopsin; D019204:GTP-Binding Proteins