Positive versus negative modulation of different endogenous chemokines for CC-chemokine receptor 1 by small molecule agonists through allosteric versus orthosteric binding.
7 transmembrane-spanning (7TM) chemokine receptors having multiple endogenous ligands offer special opportunities to understand the molecular basis for allosteric mechanisms. Thus, CC-chemokine receptor 1 (CCR1) binds CC-chemokine 3 and 5 (CCL3 and CCL5) with K(d) values of 7.3 and 0.16 nm, respectively, as determined in homologous competition binding assays. However, CCL5 appears to have a >10,000-fold lower affinity in competition against (125)I-CCL3. Mutational mapping revealed that CCL3 and CCL5 both are strongly affected by systematic truncations of the N-terminal extension, whereas only CCL5 and not CCL3 activation is affected by substitutions in the main ligand binding pocket including the conserved GluVII:06 anchor point. A series of metal ion chelator complexes were found to act as full agonists on CCR1 and to be critically affected by the same substitutions in the main ligand binding pocket as CCL5 but not by mutations in the extracellular domain. In agreement with the overlapping binding sites, the small non-peptide agonists displaced radiolabeled CCL5 with high affinity. Interestingly, the same compounds acted as allosteric enhancers of the binding of CCL3, with which they did not overlap in binding site, leading to an increased B(max) and affinity of this chemokine mainly due to an increased association rate. It is concluded that a small molecule agonist through binding deep in the main ligand binding pocket can act as an allosteric enhancer for one endogenous chemokine and at the same time as a competitive blocker of the binding of another endogenous chemokine.
Jensen
Pia C
PC
Department of Neuroscience and Pharmacology, Copenhagen University, Blegdamsvej 3, DK-2200, Copenhagen, Denmark.
Thiele
Stefanie
S
Ulven
Trond
T
Schwartz
Thue W
TW
Rosenkilde
Mette M
MM
D000495:Allosteric Site; D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D054405:Chemokine CCL3 / Q000737:chemistry; D018946:Chemokine CCL5 / Q000737:chemistry; D002522:Chlorocebus aethiops; D005786:Gene Expression Regulation; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D054389:Receptors, CCR1 / Q000737:chemistry / Q000502:physiology*
C515429:CCL3 protein, human; C483024:CCL5 protein, human; C515300:CCR1 protein, human; D054405:Chemokine CCL3; D018946:Chemokine CCL5; D054389:Receptors, CCR1