Identification of critical residues in loop E in the 5-HT(3AS)R binding site

BACKGROUND: The serotonin type 3 receptor (5-HT(3)R) is a member of a superfamily of ligand gated ion channels. All members of this family share a large degree of sequence homology and presumably significant structural similarity. A large number of studies have explored the structure-function relationships of members of this family, particularly the nicotinic and GABA receptors. This information can be utilized to gain additional insights into specific structural and functional features of other receptors in this family. RESULTS: Thirteen amino acids in the mouse 5-HT(3AS)R that correspond to the putative E binding loop of the nicotinic α7 receptor were chosen for mutagenesis. Due to the presence of a highly conserved glycine in this region, it has been suggested that this binding loop is comprised of a hairpin turn and may form a portion of the ligand-binding site in this ion channel family. Mutation of the conserved glycine (G147) to alanine eliminated binding of the 5-HT(3)R antagonist [(3)H]granisetron. Three tyrosine residues (Y140, Y142 and Y152) also significantly altered the binding of 5-HT(3)R ligands. Mutations in neighboring residues had little or no effect on binding of these ligands to the 5-HT(3AS)R. CONCLUSION: Our data supports a role for the putative E-loop region of the 5-HT(3)R in the binding of 5-HT, mCPBG, d-tc and lerisetron. 5-HT and mCPBG interact with Y142, d-tc with Y140 and lerisetron with both Y142 and Y152. Our data also provides support for the hypothesis that this region of the receptor is present in a loop structure

(Z)-N-[3-(2-Methoxy­phen­yl)-4-phenyl-2,3-dihydro­thia­zol-2-yl­idene]-2-methyl­benzamide

In the title mol­ecule, C24H20N2O2S, the thia­zole and amide groups are essentially coplanar. The thia­zole ring forms dihedral angles of 61.62 (4) and 26.75 (5)° with the benzene rings of the methoxy­phenyl and methyl­phenyl groups, respectively, and 33.69 (6)° with the phenyl ring. The crystal packing is stabilized by inter­molecular C—H⋯O hydrogen bonds, forming a three-dimensional network

(Z)-N-[3-(2-Methoxy­phen­yl)-4-phenyl-2,3-dihydro­thia­zol-2-yl­idene]-4-methyl­benzamide

Geometric parameters of the title compound, C24H20N2O2S, are in the usual ranges. The central heterocycle makes dihedral angles of 41.29 (4) and 72.94 (5)° with the phenyl ring and the methoxy­phenyl ring, respectively

Functional group interactions of a 5-HT3R antagonist

Background: Lerisetron, a competitive serotonin type 3 receptor (5-HT 3R) antagonist, contains five functional groups capable of interacting with amino acids in the 5-HT3R binding site. Site directed mutagenesis studies of the 5-HT3AR have revealed several amino acids that are thought to form part of the binding domain of this receptor. The specific functional groups on the ligand that interact with these amino acids are, however, unknown. Using synthetic analogs of lerisetron as molecular probes in combination with site directed mutagenesis, we have identified some of these interactions and have proposed a model of the lerisetron binding site. Results: Two analogs of lerisetron were synthesized to probe 5-HT3R functional group interactions with this compound. Analog 1 lacks the N1 benzyl group of lerisetron and analog 2 contains oxygen in place of the distal piperazine nitrogen. Both analogs show significantly decreased binding affinity to wildtype 5-HT3ASRs. Mutations at W89, R91, Y142 and Y152 produced significant decreases in binding compared to wildtype receptors. Binding affinities of analogs 1 and 2 were altered only by mutations at W89, and Y152. Conclusions: Based on the data obtained for lerisetron and analogs 1 and 2, we have proposed a tentative model of the lerisetron binding pocket of the 5-HT3ASR. According to this model, The N-benzyl group interacts in a weak interaction with R91 while the benzimidazole group interacts with W89. Our data support an interaction of the distal amino nitrogen with Y142 and Y152

Functional group interactions of a 5-HT(3)R antagonist

BACKGROUND: Lerisetron, a competitive serotonin type 3 receptor (5-HT(3)R) antagonist, contains five functional groups capable of interacting with amino acids in the 5-HT(3)R binding site. Site directed mutagenesis studies of the 5-HT(3A)R have revealed several amino acids that are thought to form part of the binding domain of this receptor. The specific functional groups on the ligand that interact with these amino acids are, however, unknown. Using synthetic analogs of lerisetron as molecular probes in combination with site directed mutagenesis, we have identified some of these interactions and have proposed a model of the lerisetron binding site. RESULTS: Two analogs of lerisetron were synthesized to probe 5-HT(3)R functional group interactions with this compound. Analog 1 lacks the N1 benzyl group of lerisetron and analog 2 contains oxygen in place of the distal piperazine nitrogen. Both analogs show significantly decreased binding affinity to wildtype 5-HT(3AS)Rs. Mutations at W89, R91, Y142 and Y152 produced significant decreases in binding compared to wildtype receptors. Binding affinities of analogs 1 and 2 were altered only by mutations at W89, and Y152. CONCLUSIONS: Based on the data obtained for lerisetron and analogs 1 and 2, we have proposed a tentative model of the lerisetron binding pocket of the 5-HT(3AS)R. According to this model, The N-benzyl group interacts in a weak interaction with R91 while the benzimidazole group interacts with W89. Our data support an interaction of the distal amino nitrogen with Y142 and Y152

Artificial Neural Network for Location Estimation in Wireless Communication Systems

In a wireless communication system, wireless location is the technique used to estimate the location of a mobile station (MS). To enhance the accuracy of MS location prediction, we propose a novel algorithm that utilizes time of arrival (TOA) measurements and the angle of arrival (AOA) information to locate MS when three base stations (BSs) are available. Artificial neural networks (ANN) are widely used techniques in various areas to overcome the problem of exclusive and nonlinear relationships. When the MS is heard by only three BSs, the proposed algorithm utilizes the intersections of three TOA circles (and the AOA line), based on various neural networks, to estimate the MS location in non-line-of-sight (NLOS) environments. Simulations were conducted to evaluate the performance of the algorithm for different NLOS error distributions. The numerical analysis and simulation results show that the proposed algorithms can obtain more precise location estimation under different NLOS environments

Applying Rprop Neural Network for the Prediction of the Mobile Station Location

Wireless location is the function used to determine the mobile station (MS) location in a wireless cellular communications system. When it is very hard for the surrounding base stations (BSs) to detect a MS or the measurements contain large errors in non-line-of-sight (NLOS) environments, then one need to integrate all available heterogeneous measurements to increase the location accuracy. In this paper we propose a novel algorithm that combines both time of arrival (TOA) and angle of arrival (AOA) measurements to estimate the MS in NLOS environments. The proposed algorithm utilizes the intersections of two circles and two lines, based on the most resilient back-propagation (Rprop) neural network learning technique, to give location estimation of the MS. The traditional Taylor series algorithm (TSA) and the hybrid lines of position algorithm (HLOP) have convergence problems, and even if the measurements are fairly accurate, the performance of these algorithms depends highly on the relative position of the MS and BSs. Different NLOS models were used to evaluate the proposed methods. Numerical results demonstrate that the proposed algorithms can not only preserve the convergence solution, but obtain precise location estimations, even in severe NLOS conditions, particularly when the geometric relationship of the BSs relative to the MS is poor

Intersubunit Interactions at Putative Sites of Ethanol Action in the M3 and M4 Domains of the NMDA Receptor GluN1 and GluN2B Subunits

Background and Purpose: The N-methyl-D-aspartate (NMDA) receptor is an important target of alcohol action in the brain. Recent studies in this laboratory have demonstrated that alcohol-sensitive positions in the intersubunit interfaces of the M3 and M4 domains of GluN1 and GluN2A subunits interact with respect to ethanol sensitivity and receptor kinetics, and that alcohol-sensitive positions in the M domains of GluN2A and GluN2B subunits differ. In this study we tested for interactions among alcohol-sensitive positions at the M domain intersubunit interfaces in GluN1/GluN2B NMDA receptors. Experimental Approach: We used whole-cell patch-clamp recording in tsA201 cells expressing tryptophan substitution mutants at ethanol-sensitive positions in the GluN1 and GluN2B NMDA receptor subunits to test for interactions among positions. Key Results: Six pairs of positions in GluN1/GluN2B significantly interacted to regulate ethanol inhibition: Gly638/Met824, Gly638/Leu825, Phe639/Leu825, Phe639/Gly826, Met818/Phe637 and Val820/Phe637. Tryptophan substitution at Met824 or Leu825 in GluN2B did not alter ethanol sensitivity but interacted with positions in the GluN1 M3 domain to regulate ethanol action, whereas tryptophan substitution at Gly638, which is the cognate of an ethanol-sensitive position in GluN2A, did not alter ethanol sensitivity or interact with positions in GluN1. Two and three pairs of positions interacted to regulate glutamate steady-state and peak current EC50, respectively, and one pair interacted with respect to macroscopic desensitization. Conclusions: Despite highly-conserved M domain sequences and similar ethanol sensitivity in the GluN2A and GluN2B subunits, the manner in which these subunits interact with the GluN1 subunit to regulate ethanol sensitivity and receptor kinetics differs

Chemical Scale Studies of the Phe-Pro Conserved Motif in the Cys Loop of Cys

The functions of two conserved residues, Phe^(135) and Pro^(136), located at the apex of the Cys loop of the nicotinic acetylcholine receptor are investigated. Both residues were substituted with natural and unnatural amino acids, focusing on the role of aromaticity at Phe^(135), backbone conformation at Pro^(136), side chain polarity and volume, and the specific interaction between the aromatic side chain and the proline. NMR spectroscopy studies of model peptides containing proline and unnatural proline analogues following a Phe show a consistent increase in the population of the cis conformer relative to peptides lacking the Phe. In the receptor, a strong interaction between the Phe and Pro residues is evident, as is a strong preference for aromaticity and hydrophobicity at the Phe site. A similar influence of hydrophobicity is observed at the proline site. In addition, across a simple homologous series of proline analogues, the results reveal a correlation between receptor function and cis bias at the proline backbone. This could suggest a significant role for the cis proline conformer at this site in receptor function