The formyl peptide receptor (FPR) 1 is a chemoattractant G protein-coupled receptor found on the surface of phagocytes. It is thought to play an important role in allowing phagocytic cells to recognize the presence of bacteria (1), which are a source of formyl peptides (2, 3). In addition, it recognizes and is activated by peptides derived from the GP-41 envelope protein of the human immunodeficiency virus type I (HIV-1) (4, 5). Recent studies with FPR-deficient mice indicate that they exhibit an increased susceptibility to infection with Listeria monocytogenes and that neutrophils from these knockout mice fail to exhibit chemotaxis in response to fMLF (6).The formyl peptide receptor was originally identified based on its ability to bind the formylated peptide, fMLF (1). Six different chemotactic peptides have been isolated from Escherichia coli, including fMLF (3), but the only similarity between them was an NH 2 -terminal formyl methionine, suggesting that this moiety is highly important in binding to FPR. Studies using NH 2 -terminal analogs of MLF had indicated that the formyl group had significant effects on the ligand binding affinity for neutrophil FPR. Free amino, desamino, and acetylated derivatives of MLF were all 3000-fold lower in affinity than fMLF (7). Substitution of the formyl group of fMLF with a tert-butyloxycarbonyl group made the ligand an antagonist of low affinity (8). However, the formyl group may be less essential than originally thought. N-Butyloxycarbonyl MLF exhibits agonist activity (9) with an affinity similar to fMLF, and phenyl and tolyl isourea derivatives of MLF exhibit activity similar to or greater than fMLF (10). On the other hand, most aliphatic isourea derivatives of MLF exhibit low affinity antagonist activity similar to what is observed with tert-butyloxycarbonyl-MLF (10). This difference indicates that FPR exhibits a high degree of specificity for NH 2 -terminal modifications of MLF, and that the specificity for the formyl group is not absolute. In addition, other reports have indicated that non-formylated pentapeptides can activate FPR. Both MNleLFF and MMWLL are effective activators of FPR (11,12), and acetyl-MNleLFF is more potent than fMLF (12), indicating that these pentapeptides exhibit somewhat different NH 2 -terminal specificities than does MLF.We have previously shown that the formyl peptide binding site maps to several membrane-spanning regions (13-14). Ten residues which affect fMLF binding have been mapped to transmembrane domains II-VII (13), including residues Leu-78 (II-17, helix II, residue 17 of 26 transmembrane-spanning residues in the nomenclature used throughout this text), Asp-106 (III-8), Leu-109 (III-11), Thr-157 (IV-18), Arg-201 (V-2), Ile-204 (V-5), , , and Phe-291 (VII-11). In addition, photo-cross-linking data suggest that the leucine side chain of fMLF is probably located close to FPR 93 VRK 95 , which is at the COOH terminus of helix II (14).Human FPR is one of three receptors in the human FPR family, which includes, FPR, the lipoxin A 4 re...

We have uncovered a significant allosteric response of the D 2 dopamine receptor to physiologically relevant concentrations of sodium (140 mM Our findings demonstrate how key interactions can be modulated by occupancy at an allosteric site and are consistent with a mechanism in which sodium binding enhances the affinity of selected ligands through dynamic changes that increase accessibility of substituted benzamides and 1,4-DAP ligands to the orthosteric site and accessibility of 1,4-DAPs to V2.61(91)F.Sodium ions have been shown to modulate dopamine receptors, and allosteric modulation by sodium ions has been shown to drive the conformational equilibrium of heterotrimeric G protein-coupled receptors (GPCRs) toward an agonist low-affinity state (for review, see Schetz, 2005). In dopamine receptors, like in other heterotrimeric GPCRs, the highly conserved and negatively charged aspartic acid at position 2.50 (the generic numbering system is defined in Ballesteros and Weinstein, 1995) has been identified as a sodium interaction site. For example, charge-neutralizing mutations in the D 2 or the D 4 receptor [e.g., D2.50(80)N or D2.50(80)A] make them sodium-insensitive, whereas a charge-sparing mutation [e.g., D2.50(80)E] retains much of the sodium sensitivity (Neve et al

Conserved serines of transmembrane segment (TM) five (TM5) are critical for the interactions of endogenous catecholamines with ␣ 1 -and ␣ 2 -adrenergic, ␤ 2 -adrenergic, and D1, D2, and D3 dopamine receptors. The unique high-affinity interaction of the D4 dopamine receptor subtype with both norepinephrine and dopamine, and the fact that TM5 serine interactions have never been studied for this receptor subtype, led us to investigate the interactions of ligands with D4 receptor TM5 serines. Serine-to-alanine mutations at positions 5.42 and 5.46 drastically decreased affinities of dopamine and norepinephrine for the D4 receptor. The D4-S5.43A receptor mutant had substantially reduced affinity for norepinephrine, but a modest loss of affinity for dopamine. In functional assays of cAMP accumulation, norephinephrine was unable to activate any of the mutant receptors, even though the agonist quinpirole displayed wild-type functional properties for all of them. Dopamine was unable to activate the S5.46A mutant and had reduced potency for the S5.43A mutant and reduced potency and efficacy for the S5.42A mutant. In contrast, Ro10-4548 [RAC-2Ј-2-hydroxy-3-4-(4-hydroxy-2-methoxyphenyl)-1-piperazinyl-propoxy-acetanilide], a catechol-like antagonist of the wild-type receptor unexpectedly functions as an agonist of the S5.43A mutant. Other noncatechol ligands had similar properties for mutant and wild-type receptors. This is the first example of a dopamine receptor point mutation selectively changing the receptor's interaction with a specific antagonist to that of an agonist, and together with other data, provides evidence, supported by molecular modeling, that catecholamine-type agonism is induced by different ligand-specific configurations of intermolecular H-bonds with the TM5 conserved serines.The D4 dopamine receptor has had a checkered history of popularity. It was for a time believed to be the ideal target for an atypical antipsychotic drug (for review see Schetz and Sibley, 2007;Schetz, 2009). The D4 receptor has also been pursued as a drug target for treating attention-deficit hyperactivity disorder (ADHD) and erectile dysfunction, but these possibilities remain controversial. A D4 polymorphic variant (D4.7) was reported to be hyporesponsive to dopamine and associated with a higher risk for ADHD (LaHoste et al., 1996). However, the relevance of a low-magnitude hyporesponsiveness is unclear, and the association of the D4.7 polymorphic variant has not always been replicated by different laboratories (for a review see Schetz and Sibley, 2007) with some studies even suggest-

Efforts to develop ligands that distinguish between clinically relevant 5-HT2A and 5-HT2C serotonin receptor subtypes have been challenging, because their sequences have high homology. Previous studies reported that a novel aplysinopsin belonging to a chemical class of natural products isolated from a marine sponge was selective for the 5-HT2C over the 5-HT2A receptor subtype. Our goal was to explore the 5-HT2A/2C receptor structure-affinity relationships of derivatives based on the aplysinopsin natural product pharmacophore. Twenty aplysinopsin derivatives were synthesized, purified and tested for their affinities for cloned human serotonin 5-HT1A, 5-HT2A and 5-HT2C receptor subtypes. Four compounds in this series had >30-fold selectivity for 5-HT2A or 5-HT2C receptors. The compound (E)-5-((5,6-dichloro-1H-indol-3-yl)methylene)-2-imino-1,3-dimethylimidazolidin-4-one (UNT-TWU-22, 16) had approximately 2100-fold selectivity for the serotonin 5-HT2C receptor subtype: an affinity for 5-HT2C equal to 46 nM and no detectable affinity for the 5-HT1A or 5-HT2A receptor subtypes. The two most important factors controlling 5-HT2A or 5-HT2C receptor subtype selectivity were the combined R1, R3-alkylation of the imidazolidinone ring and the type and number of halogens on the indole ring of the aplysinopsin pharmacophore.

The D2 dopamine receptor is an important therapeutic target for the treatment of psychotic, agitated, and abnormal behavioral states. To better understand the specific interactions of subtype-selective ligands with dopamine receptor subtypes, seven ligands with high selectivity (>120-fold) for the D4 subtype of dopamine receptor were tested on wild-type and mutant D2 receptors. Five of the selective ligands were observed to have 21-fold to 293-fold increases in D2 receptor affinity when three non-conserved amino acids in TM2 and TM3 were mutated to the corresponding D4 amino acids. The two ligands with the greatest improvement in affinity for the D2 mutant receptor [i.e., 3-{[4-(4-iodophenyl) piperazin-1-yl]methyl}-1H-pyrrolo[2,3-b]pyridine (L-750,667) and 1-[4-iodobenzyl]-4-[N-(3-isopropoxy-2-pyridinyl)-N-methyl]-aminopiperidine (RBI-257)] were investigated in functional assays. Consistent with their higher affinity for the mutant than for the wild-type receptor, concentrations of L-750,667 or RBI-257 that produced large reductions in the potency of quinpirole’s functional response in the mutant did not significantly reduce quinpirole’s functional response in the wild-type D2 receptor. In contrast to RBI-257 which is an antagonist at all receptors, L-750,667 is a partial agonist at the wild-type D2 but an antagonist at both the mutant D2 and wild-type D4 receptors. Our study demonstrates for the first time that the TM2/3 microdomain of the D2 dopamine receptor not only regulates the selective affinity of ligands, but in selected cases can also regulate their function. Utilizing a new docking technique that incorporates receptor backbone flexibility, the three non-conserved amino acids that encompass the TM2/3 microdomain were found to account in large part for the differences in intermolecular steric contacts between the ligands and receptors. Consistent with the experimental data, this model illustrates the interactions between a variety of subtype-selective ligands and the wild-type D2, mutant D2, or wild-type D4 receptors.