The activation mechanism of chemokine receptor CCR5 involves common structural changes but a different network of interhelical interactions relative to rhodopsin.
In G protein-coupled receptors (GPCRs), the interaction between the cytosolic ends of transmembrane helix 3 (TM3) and TM6 was shown to play an important role in the transition from inactive to active states. According to the currently prevailing model, constructed for rhodopsin and structurally related receptors, the arginine of the conserved "DRY" motif located at the cytosolic end of TM3 (R3.50) would interact with acidic residues in TM3 (D/E3.49) and TM6 (D/E6.30) at the resting state and shift out of this polar pocket upon agonist stimulation. However, 30% of GPCRs, including all chemokine receptors, contain a positively charged residue at position 6.30 which does not support an interaction with R3.50. We have investigated the role of R6.30 in this receptor family by using CCR5 as a model. R6.30D and R6.30E substitutions, which allow an ionic interaction with R3.50, resulted in an almost silent receptor devoid of constitutive activity and strongly impaired in its ability to bind chemokines but still able to internalize. R6.30A and R6.30Q substitutions, allowing weaker interactions with R3.50, preserved chemokine binding but reduced the constitutive activity and the functional response to chemokines. These results indicate that the constitutive and ligand-promoted activity of CCR5 can be modified by modulating the interaction between the DRY motif in TM3 and residues in TM6 suggesting that the overall structure and activation mechanism are well conserved in GPCRs. However, the molecular interactions locking the inactive state must be different in receptors devoid of D/E6.30.
Springael
Jean-Yves
JY
Institut de Recherche Interdisciplinaire en Biologie Humaine et Moléculaire (IRIBHM), ULB Campus Erasme, 808 Route de Lennik, B-1070 Brussels, Belgium.
de Poorter
Cédric
C
Deupi
Xavier
X
Van Durme
Joost
J
Pardo
Leonardo
L
Parmentier
Marc
M
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002417:Cattle; D054407:Chemokine CCL4; D019295:Computational Biology; D006224:Cricetinae; D003412:Cricetulus; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D004705:Endocytosis / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008024:Ligands; D019402:Macrophage Inflammatory Proteins / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D019713:Receptors, CCR5 / Q000737:chemistry* / Q000378:metabolism*; D012243:Rhodopsin / Q000737:chemistry* / Q000378:metabolism*; D013329:Structure-Activity Relationship
D054407:Chemokine CCL4; D008024:Ligands; D019402:Macrophage Inflammatory Proteins; D050505:Mutant Proteins; D019713:Receptors, CCR5; D012243:Rhodopsin; D020928:Mitogen-Activated Protein Kinases