Roteincoupled receptor kinases and arrestins, which promote receptor internalization. Some chemokine ligands have distinct efficacies for stimulating intracellular signaling and internalization of CCR5 [5]. HIV binding to CCR5 must stabilize a receptor conformation that induces the fusion conformation of Env. HIV also stimulates CCR5-dependent cellular signaling [6,7,8]. The structures of a small number of GPCR proteins have been determined in inverse agonist-bound inactive conformations [9,10,11,12] and in complexes with agonist and a G protein or G protein mimetic, which stabilize active receptor conformations [13,14,15]. The crystal structures support hypotheses that amino acids that are highly conserved among GPCRs form distinct intramolecular interactions in active and inactive receptor conformations and act as activation “switches” [4,16,17,18].Constitutively Active CCR5 Receptor ConformationsSupporting the switch hypothesis, mutation of the Asp3.49 and Arg3.50 residues of the conserved DRY (Asp-Arg-Tyr) motif, in transmembrane segment (TMS) 3, stabilizes mutant CAL120 receptors in activated conformations, which stimulate cellular signaling in the absence of agonist [19]. Different mutations of the Thr2.56(82) and Pro2.58(84) residues of the conserved TxP motif, stabilized CCR5 mutants in inactive [20] or constitutively active conformations [21]. A naturally-occurring Arg6.32(225)Gln mutation causes partial Licochalcone-A web constitutive activity in CCR5 [22]. The CCR5 conformation(s) that induce the fusogenic changes in Env are not known. Binding of the gp120 subunit of Env to CCR5 stimulates intracellular signaling [6,7,8], suggesting that HIV stabilizes activated CCR5 conformations that activate G proteins and other cytosolic signaling proteins. On the other hand, CCR5 receptors with inactivating mutations, which uncouple CCR5 from activation of G protein and other signaling pathways, mediated Env-dependent membrane fusion [23,24,25], suggesting that inactive CCR5 conformations mediate HIV entry. Small molecule CCR5-binding anti-HIV drugs are inverse agonists. HIV strains that are resistant to CCR5 “blockers” use drug-bound CCR5 to infect cells [26,27,28,29], suggesting that a drugstabilized, inactive receptor conformation mediates infection. Thus, inactive CCR5 conformation(s) mediate HIV infection and we hypothesized that activated conformations that stimulate G protein signaling would be poor mediators of Env-directed membrane fusion. We have investigated the ability of activated conformations of CCR5 to mediate Env-directed membrane fusion by mutating conserved “switch” residues of the human CCR5 chemokine receptor. Mutation of Asp3.49(125) and Arg6.32(225) did not increase constitutive activity. CCR5 23977191 mutants with Pro or Lys substituted for Thr2.56(82) showed high basal cellular signaling, which was not increased by stimulation with MIP-1b. The Thr2.56(82)Lys mutation decreased cell surface CCR5 protein, whereas the Thr2.56(82)Pro mutation did not. Constitutively active CCR5 receptors differed in their ability to mediate Env-directed membrane fusion. Our results suggest that Pro and Lys substitutions in position 2.56(82) stabilize distinct activated CCR5 conformations that differ in their localization at the cell surface and in their ability to induce HIV Env-dependent membrane fusion.was stably transfected into both of these cell lines. Recombinant human chemokine MIP-1b (CCL4) was purchased from Peprotec (Rocky Hill, NJ).Generation of Mutan.Roteincoupled receptor kinases and arrestins, which promote receptor internalization. Some chemokine ligands have distinct efficacies for stimulating intracellular signaling and internalization of CCR5 [5]. HIV binding to CCR5 must stabilize a receptor conformation that induces the fusion conformation of Env. HIV also stimulates CCR5-dependent cellular signaling [6,7,8]. The structures of a small number of GPCR proteins have been determined in inverse agonist-bound inactive conformations [9,10,11,12] and in complexes with agonist and a G protein or G protein mimetic, which stabilize active receptor conformations [13,14,15]. The crystal structures support hypotheses that amino acids that are highly conserved among GPCRs form distinct intramolecular interactions in active and inactive receptor conformations and act as activation “switches” [4,16,17,18].Constitutively Active CCR5 Receptor ConformationsSupporting the switch hypothesis, mutation of the Asp3.49 and Arg3.50 residues of the conserved DRY (Asp-Arg-Tyr) motif, in transmembrane segment (TMS) 3, stabilizes mutant receptors in activated conformations, which stimulate cellular signaling in the absence of agonist [19]. Different mutations of the Thr2.56(82) and Pro2.58(84) residues of the conserved TxP motif, stabilized CCR5 mutants in inactive [20] or constitutively active conformations [21]. A naturally-occurring Arg6.32(225)Gln mutation causes partial constitutive activity in CCR5 [22]. The CCR5 conformation(s) that induce the fusogenic changes in Env are not known. Binding of the gp120 subunit of Env to CCR5 stimulates intracellular signaling [6,7,8], suggesting that HIV stabilizes activated CCR5 conformations that activate G proteins and other cytosolic signaling proteins. On the other hand, CCR5 receptors with inactivating mutations, which uncouple CCR5 from activation of G protein and other signaling pathways, mediated Env-dependent membrane fusion [23,24,25], suggesting that inactive CCR5 conformations mediate HIV entry. Small molecule CCR5-binding anti-HIV drugs are inverse agonists. HIV strains that are resistant to CCR5 “blockers” use drug-bound CCR5 to infect cells [26,27,28,29], suggesting that a drugstabilized, inactive receptor conformation mediates infection. Thus, inactive CCR5 conformation(s) mediate HIV infection and we hypothesized that activated conformations that stimulate G protein signaling would be poor mediators of Env-directed membrane fusion. We have investigated the ability of activated conformations of CCR5 to mediate Env-directed membrane fusion by mutating conserved “switch” residues of the human CCR5 chemokine receptor. Mutation of Asp3.49(125) and Arg6.32(225) did not increase constitutive activity. CCR5 23977191 mutants with Pro or Lys substituted for Thr2.56(82) showed high basal cellular signaling, which was not increased by stimulation with MIP-1b. The Thr2.56(82)Lys mutation decreased cell surface CCR5 protein, whereas the Thr2.56(82)Pro mutation did not. Constitutively active CCR5 receptors differed in their ability to mediate Env-directed membrane fusion. Our results suggest that Pro and Lys substitutions in position 2.56(82) stabilize distinct activated CCR5 conformations that differ in their localization at the cell surface and in their ability to induce HIV Env-dependent membrane fusion.was stably transfected into both of these cell lines. Recombinant human chemokine MIP-1b (CCL4) was purchased from Peprotec (Rocky Hill, NJ).Generation of Mutan.

Roteincoupled receptor kinases and arrestins, which promote receptor internalization. Some chemokine

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