HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Almaula, N. Articles by Sealfon, S. C. Search for Related Content PubMed PubMed Citation Articles by Almaula, N. Articles by Sealfon, S. C. Social Bookmarking                      What's this?

Volume 271, Number 25, Issue of June 21, 1996 pp. 14672-14675
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

---

COMMUNICATION:
Mapping the Binding Site Pocket of the Serotonin 5-Hydroxytryptamine_2A Receptor
Ser^3.36(159) PROVIDES A SECOND INTERACTION SITE FOR THE PROTONATED AMINE OF SEROTONIN BUT NOT OF LYSERGIC ACID DIETHYLAMIDE OR BUFOTENIN^*

(Received for publication, April 17, 1996)

Niva Almaula , Barbara J. Ebersole ^§¶, Daqun Zhang , Harel Weinstein ^¶ and Stuart C. Sealfon ^''

From the  Fishberg Research Center in Neurobiology, Departments of ^§ Anesthesiology,  Physiology and Biophysics, ^¶ Pharmacology, and ^'' Neurology, Mount Sinai School of Medicine, New York, New York 10029

ABSTRACT

INTRODUCTION

MATERIALS AND METHODS

RESULTS AND DISCUSSION

FOOTNOTES

Acknowledgments

REFERENCES

ABSTRACT

Like other amine neurotransmitters that activate G-protein-coupled receptors, 5-hydroxytryptamine (5-HT) binds to the 5-HT_2A receptor through the interaction of its cationic primary amino group with the conserved Asp^3.32(155) in transmembrane helix 3. Computational experiments with a 5-HT_2A receptor model suggest that the same functional group of 5-hydroxytryptamine also forms a hydrogen bond with the side chain of Ser^3.36(159), which is adjacent in space to Asp^3.32(155). However, other 5-HT_2A receptor ligands like lysergic acid diethylamide (LSD), in which the amine nitrogen is embedded in a heterocycle, or N,N-dimethyl 5-HT, in which the side chain is a tertiary amine, are found in the computational simulations to interact with the aspartate but not with the serine, due mainly to steric hindrance. The predicted difference in the interaction of various ligands in the same receptor binding pocket was tested with site-directed mutagenesis of Ser^3.36(159)  Ala and Ser^3.36(159)  Cys. The alanine substitution led to an 18-fold reduction in 5-HT affinity and the cysteine substitution to an intermediate 5-fold decrease. LSD affinity, in contrast, was unaffected by either mutation. N,N-Dimethyl 5-HT affinity was unaffected by the cysteine mutation and had a comparatively small 3-fold decrease in affinity for the alanine mutant. These findings identify a mode of ligand-receptor complexation that involves two receptor side chains interacting with the same functional group of specific serotonergic ligands. This interaction serves to orient the ligands in the binding pocket and may influence the degree of receptor activation.

---

INTRODUCTION

One goal of structure-activity studies of G-protein-coupled receptors (GPCR)¹ is to develop an understanding of the nature and consequences of ligand-receptor interactions at a molecular level. The serotonin 5-HT_2A receptor is a member of the GPCR superfamily for which such studies have identified key interactions in the ligand-receptor complexes (1, 2, 3, 4, 5, 6, 7, 8, 9). One notable group of ligands for this receptor are the serotonergic hallucinogens, such as LSD (lysergic acid diethylamide) and N,N-dimethyl 5-HT (bufotenin), which have high affinity for the 5-HT_2A receptor. Studying the receptor's binding pocket and identifying the molecular mechanisms that determine ligand affinity, specificity, and coupling efficiency may help elucidate the basis for the special biological effects of these chemicals.

The principal binding determinants of neurotransmitter GPCRs have been most fully elucidated in the adrenergic receptors (for review see Refs. 10 and 11), where they are located within the helical transmembrane domains. The 5-HT_2A receptor, like the other receptors for biogenic amines, including the adrenergic, dopaminergic, and muscarinic receptors, has an aspartate residue at a homologous location in the putative third transmembrane helix (TMH) domain (Ref. 12; see Fig. 1). Site-directed mutagenesis studies with these receptors indicate that, for most ligands, an interaction between the basic nitrogen of the ligand and the carboxyl side chain of the TMH 3 aspartate stabilizes ligand binding (5, 13, 14, 15, 16, 17).

---

Fig. 1. Helical net representation of TMH 3 of the 5-HT_2A receptor showing the position of the conserved aspartate in neurotransmitter GPCRs, Asp^3.32(155), and of Ser^3.36(159).

---

Simulations of ligand-receptor complexes of the 5-HT_2A receptor using a three-dimensional computational model (6, 7) suggest a complex array of interactions connecting TMH 3 side chains and specific ligands. The same charged amino group of 5-hydroxytryptamine that interacts with the TMH 3 aspartate is predicted to form a hydrogen bond with the side chain of a second TMH 3 locus, Ser^3.36(159). In the molecular model of the receptor, this residue is positioned on the same face of the helix as Asp^3.32(155). It forms a hydrogen bond to the backbone carbonyl of the residue at position i  4 from it, as expected (17). The simulations show a very favorable positioning of the cationic amine group of 5-HT for hydrogen bonding both the aspartate and the serine. However, some other serotonergic ligands, such as LSD and N,N-dimethyl 5-HT, are found to be unable to hydrogen bond that serine because of the steric hindrance introduced by the groups surrounding the amine in the ligand. Extensive simulations show that the ligands in which the amino group is ring-embedded or dimethyl-substituted would interact only with the aspartate side chain.² Because these predictions, if validated, provide a fine resolution mapping of this component of the binding pocket that may explain why ligands vary in their capacity to activate the receptor, this hypothesis was tested by mutating Ser^3.36(159)  Ala and Ser^3.36(159)  Cys. The results from ligand binding experiments with the mutant receptors were analyzed with respect to the inferences from molecular dynamic simulations of the receptor-ligand complexes.

---

MATERIALS AND METHODS

Chemicals

LSD and N,N-dimethyl 5-HT were obtained from NIDA, National Institutes of Health. All other unlabeled ligands were from Sigma or Research Biochemicals International (Natick, MA).

Receptor Numbering Scheme

Residues are numbered according to a consensus numbering scheme described in detail elsewhere (18). The TMH 3 residues are numbered in reference to the most conserved residue in this helix, which is the arginine at the bottom of the helix. This most conserved locus is designated 3.50; adjacent residues are 3.49 and 3.51. The residue number in parentheses indicates the amino acid identity using standard amino-terminal based numbering. Thus the TMH 3 aspartate conserved among neurotransmitters is designated Asp^3.32(155) in the 5-HT_2A receptor, and the serine studied here is Ser^3.36(159).

DNA Constructs and Transfection

The cDNA clone encoding the human 5-HT_2A receptor was graciously provided by Dr. Alan Saltzman (19). Mutations were introduced as described previously (9). The expression vectors, pcDNA-Amp (binding assays) or pcDNA-3 (functional assays; Invitrogen, San Diego, CA) were used to transfect COS-1 cells (ATCC, Rockville, MD) using Lipofectamine (Life Technologies, Inc.).

Coupling and Ligand Binding Assays

Hydrolysis of [³H]phosphatidylinositol was assayed as described previously (9). Saturation and competition assays using [³H]ketanserin (DuPont NEN) were carried out as described previously (9). Nonspecific binding was defined with 10 µM methysergide. For competition studies, the concentration of [³H]ketanserin was 0.7-1.2 nM. Protein content was determined by the method of Lowry (20). Each binding assay tube contained 30-60 µg of membrane protein.

Data Analysis

Curve-fitting for data from saturation, competition, and phosphatidylinositol assays was carried out with the graphics software Kaleidagraph (Synergy Software, Reading, PA) as described previously (9).

Molecular Modeling of 5-HT_2A Receptor Mutants and Computational Simulations of Interactions with Ligands

The model of the transmembrane helix bundle of the 5-HT_2A receptor and its development have been reported previously (7, 22). A primary objective in the early development of this model was to reflect the pharmacological data on the structure-activity relations of 5-HT_2A receptor ligands. The close agreement between the results from computational simulations of the effects of ligand binding with this receptor model and quantitative pharmacological data (6, 7, 8, 9) supports its use to explore the role of Ser^3.36(159) in the interaction with specific ligands.

The molecular models were energy-optimized, and molecular dynamics runs were carried out with the CHARMM program (23), using the same protocol as described previously (7). 5-HT, N,N-dimethyl 5-HT, and LSD were positioned in the binding site in the same manner as described, to preserve the equivalence of their initial positioning in the binding pocket (7). The same parameters for molecular dynamic simulations were used as reported previously (7). Simulation of the ligand/receptor complexes were carried out for >200 ps, and the equilibrated structures of the ligand/receptor complex were obtained from the energy-minimized average over the final period of the simulation covering the last 100 ps, as described (7).

---

RESULTS AND DISCUSSION

Affinities of Wild-type and Mutant Receptors

The hypothesis that ligands differ in their interaction with Ser^3.36(159) was tested by mutating this residue to cysteine and to alanine and by characterizing the wild-type and mutated receptors when expressed in COS-1 cells. The receptor mutants had comparable affinities for ketanserin, as determined by saturation binding (Table I).

Table I. Binding affinities of the wild-type and Ser3.36(159) mutant receptors Kd values for ketanserin and Bmax values were obtained from saturation binding experiments (mean ± S.E. from 3-4 experiments). Ki values for 5-HT, N,N-dimethyl 5-HT, and LSD were obtained from competition binding experiments with [3H]ketanserin. Results are mean ±S.E. from 4 experiments. Receptor construct Bmax Kd for ketanserin Ki 5-HT N,N-dimethyl 5-HT LSD fmol/mg nM nM Ser3.36(159) 1009  ± 170 0.84  ± 0.14 396  ± 107 162  ± 14 0.38  ± 0.05 Ser3.36(159)  Ala 506  ± 86 1.1  ± 0.14 6960  ± 1592 645  ± 88 0.54  ± 0.13 Ser3.36(159)  Cys 921  ± 157 0.66  ± 0.04 1947  ± 528 224  ± 44 0.33  ± 0.04

The effects of the mutations studied on agonist affinity correlated fully with the expectations from the computational modeling of the wild-type and the alanine mutant complexes with the various ligands.² The affinity of 5-HT was greatly affected by the alanine substitution (18-fold decrease), and the presence of cysteine at this position caused an intermediate 5-fold decrease in affinity (Fig. 2A). In contrast, the affinity of the N,N-dimethyl congener of 5-HT, bufotenin, showed no significant change with the cysteine mutation and a comparatively small 4-fold decrease in affinity with the alanine substitution (Fig. 2B). LSD affinity was not significantly affected by either mutation (Fig. 2C).

---

Fig. 2. Competition binding curves for Ser^3.36(159) mutant receptors. The structural formulas for the compounds studied are shown, and the amine that interacts in its cationic form with the TMH 3 acidic group is indicated by an arrow. Results are representative of 4 independent experiments. A, 5-HT competition; B, N,N-dimethyl 5-HT competition; C, LSD competition.

---

The affinity of the ligands for the mutant constructs is consistent with the inference from the studies of many neurotransmitter receptors, including the 5-HT_2A receptor (5), that the interaction with Asp^3.32 provides a major component of the binding affinity. The large decrease in the affinity of 5-HT found with mutation of Ser^3.36(159) is consonant with the effect of elimination of a hydrogen bond-type interaction between the amino group of serotonin and the serine side chain. Because the Ser^3.36(159)  Cys mutant constructs were not subjected to a complete dynamic modeling, the exact mechanism for the intermediate affinity changes is less clear. Notably, the cysteine side chain is a less favorable hydrogen bond acceptor than is that of serine (24), so that the moderate effect on 5-HT affinity seen with the cysteine mutation may reflect a weaker interaction between the mutant side chain and the cationic amine group of 5-HT. In contrast, the cationic amine of LSD is embedded in a ring, as shown in Fig. 2C, and is not available for the secondary hydrogen bonding. The correspondence of the ring nitrogen of LSD to the alkyl nitrogen of 5-HT is consistent with known structure-activity data (25). The lack of effect on LSD affinity of either substitution for the wild-type serine indicates that there is no interaction between serine and LSD in the wild-type receptor. The affinity of N,N-dimethyl 5-HT is unaffected by the cysteine mutation, and a very small decrease in affinity is observed with the alanine substitution. In view of the large changes seen with the same mutations for 5-HT, the relatively small decrease in N,N-dimethyl 5-HT affinity seen with one of the mutations is likely to represent an indirect effect arising from altered positioning of other side chains in the binding pocket of the Ser  Ala mutant. Because of its dimethyl substitution, the basic nitrogen of this ligand could not hydrogen-bond to the serine and also interact with the aspartate. The comparison of the results obtained with 5-HT, N,N-dimethyl 5-HT, and LSD support the presence of a direct interaction with the serine side chain only for 5-HT.

Molecular Dynamic Simulations of Ligand-Receptor Complexes

The ligands studied in binding assays were also studied in molecular dynamics simulations of ligand-receptor complexes. The results of these simulations are shown in Fig. 3. In the 5-HT-complexed serotonin receptor model, the amino group is positioned equidistant from the side chains of the aspartate and the serine (Fig. 3A). The distance from the serine, 1.8 Å, is an appropriate distance for hydrogen bonding. In contrast, the corresponding amines both in N,N-dimethyl 5-HT (Fig. 3B) and in LSD (Fig. 3C) are located at nearly 5 Å from the serine side chain, too great a distance for efficient hydrogen bond formation. Thus, while all three agonists interact with the aspartate side chain, only 5-HT interacts with the serine.

---

Fig. 3.

Position of ligands interacting with TMH 3 obtained from molecular dynamic simulations of ligand-receptor complexes. Data were obtained from a full computational model of the ligand-complexed 5-HT_2A receptor. For clarity, only part of TMH 3 with the side chains of Asp^3.32(155) and Ser^3.36(159) is shown. Distances are the separation of the functional groups in the energy-minimized average structure resulting from the simulation with the wild-type 5-HT_2A receptor model. A, 5-HT-receptor complex; B, N,N-dimethyl 5-HT-receptor complex; C, LSD-receptor complex. The distance between Asp^3.32(155) and the cationic amine of LSD is 2.8 Å.

---

Consequences of Interaction with Ser^3.36(159)

The presence or absence of a hydrogen bond with Ser^3.36(159) plays a definable role in the positioning of agonists in the binding pocket. The ligands 5-HT and N,N-dimethyl 5-HT, for example, differ only in the presence of the dimethyl substitution of the amine nitrogen (Fig. 2, A and B). We demonstrate by congruent results of mutagenesis and computational simulations that the major effect of this substitution is to eliminate the hydrogen bond with Ser^3.36(159) and, thereby, to alter the orientation of the ligand with respect to its dominant TMH 3 site of interaction, Asp^3.32(155).

The altered positioning of structurally similar ligands may provide an explanation for their differing functional effects. Notably, both N,N-dimethyl 5-HT and LSD are partial agonists for the 5-HT_2A receptor. A variety of experiments suggest that TMH 3 provides a crucial anchor for neurotransmitter agonists and that the precise positioning of a ligand with respect to TMH 3 can determine its ability to activate the receptor. Strader et al. found that altering the length of the TMH 3 acidic side chain of the -adrenergic receptor, by mutating Asp^3.32(113)  Glu, caused some antagonists to develop partial agonist activity (21). This result shows that the capacity of the ligand to activate the receptor relates to its positioning between TMH 3 and other interaction sites. In molecular dynamic simulations of ligand-receptor complexes, we have found that partial agonists cause a smaller degree of helix rearrangement than do full agonists, whether they are structurally related to 5-HT (7) or to other families of 5-HT_2A ligands (8). It is expected, therefore, that the ability of a ligand to activate a receptor depends on the geometrical arrangement of the ligand in the ligand-receptor complex. As the presence or absence of an interaction with the second TMH 3 site in the 5-HT_2A receptor, Ser^3.36(159), alters this geometry, it can determine the differing potential of closely related compounds to activate the receptor.

The contribution of the interaction with Ser^3.36(159) in positioning the ligand and thereby determining efficacy is supported by the concentration-response curves obtained with the wild-type and Ser^3.36(159)  Ala mutant receptors. Whereas N,N-dimethyl 5-HT is a partial agonist for the wild-type receptor (Fig. 4A), the intrinsic activities of 5-HT and N,N-dimethyl 5-HT are similar for the Ser^3.36(159) receptor mutant (Fig. 4B). The intrinsic activity of N,N-dimethyl 5-HT relative to 5-HT was 0.73 ± 0.07 for the wild-type receptor and 0.96 ± 0.13 for the mutant (n = 4, p < 0.05).

---

Fig. 4. Concentration-response curves of phosphatidylinositol hydrolysis with 5-HT and N,N-dimethyl 5-HT stimulation. A, wild-type receptor; B, Ser^3.36(159)  Ala mutant receptor. Results shown are representative of 4 independent experiments.

---

We find that the free amino group of 5-HT interacts with a second side chain of TMH 3 of the serotonin 5-HT_2A receptor. To our knowledge, this is the first example of two side chains of a receptor interacting specifically with the same functional group on the ligand. The positioning of the ligands in the binding site relates to their ability to form this second hydrogen bonding interaction and can influence their capacity to activate the receptor. The results illustrate how a detailed map of the binding site pocket of the serotonin 5-HT_2A receptor obtained through combined mutagenesis and dynamic receptor modeling can lead to a fuller understanding of the molecular basis for the effects of serotonergic ligands.

FOOTNOTES

Acknowledgments

We thank Dr. Saul Maayani for helpful discussions and Irina Ivanova for superb technical assistance.

REFERENCES

1. Choudhary, M. S., Craigo, S., Roth, B. L. (1993) Mol. Pharmacol. 43, 755-761 [Abstract]
2. Choudhary, M. S., Sachs, N., Uluer, A., Glennon, R. A., Westkaemper, R. B., Roth, B. L. (1995) Mol. Pharmacol. 47, 450-457 [Abstract]
3. Choudhary, M. S., Craigo, S., Roth, B. L. (1992) Mol. Pharmacol. 42, 627-633 [Abstract]
4. Johnson, M. P., Loncharich, R. J., Baez, M., Nelson, D. L. (1994) Mol. Pharmacol. 45, 277-286 [Abstract]
5. Wang, C.-D., Gallaher, T. K., Shih, J. C. (1993) Mol. Pharmacol. 43, 931-940 [Abstract]
6. Luo, X., Zhang, D., Weinstein, H. (1994) Protein Eng. 7, 1441-1448 [Abstract/Free Full Text]
7. Zhang, D., Weinstein, H. (1993) J. Med. Chem. 36, 934-938 [CrossRef][Medline] [Order article via Infotrieve]
8. Zhang, D., Weinstein, H. (1993) Med. Chem. Res. 3, 357-369
9. Sealfon, S. C., Chi, L., Ebersole, B. J., Rodic, V., Zhang, D., Ballesteros, J. A., Weinstein, H. (1995) J. Biol. Chem. 270, 16683-16688 [Abstract/Free Full Text]
10. Kobilka, B. (1992) Annu. Rev. Neurosci. 15, 87-114 [CrossRef][Medline] [Order article via Infotrieve]
11. Strader, C. D., Fong, T. M., Tota, M. R., Underwood, D., Dixon, R. (1994) Annu. Rev. Biochem. 63, 101-132 [CrossRef][Medline] [Order article via Infotrieve]
12. Wang, C. D., Buck, M. A., Fraser, C. M. (1991) Mol. Pharmacol. 40, 168-179 [Abstract]
13. Strader, C. D., Sigal, I. S., Register, R. B., Candelore, M. R., Rands, E., Dixon, R. A. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 4384-4388 [Abstract/Free Full Text]
14. Strader, C. D., Sigal, I. S., Candelore, M. R., Rands, E., Hill, W. S., Dixon, R. A. F. (1988) J. Biol. Chem. 263, 10267-10271 [Abstract/Free Full Text]
15. Ho, B. Y., Karschin, A., Branchek, T., Davidson, N., Lester, H. A. (1992) FEBS Lett. 312, 259-262 [CrossRef][Medline] [Order article via Infotrieve]
16. Fraser, C. M., Wang, C. D., Robinson, D. A., Gocayne, J. D., Venter, J. C. (1989) Mol. Pharmacol. 36, 840-847 [Abstract]
17. Gray, T. M., Matthews, B. W. (1984) J. Mol. Biol. 175, 75-81 [CrossRef][Medline] [Order article via Infotrieve]
18. Ballesteros, J. A., Weinstein, H. (1995) Methods Neurosci. 25, 366-428
19. Saltzman, A. G., Morse, B., Whitman, M. M., Ivanshchenko, Y., Jaye, M., Felder, S. (1991) Biochem. Biophys. Res. Commun. 181, 1469-1478 [CrossRef][Medline] [Order article via Infotrieve]
20. Lowry, O. H., Rosebrough, N. J., Farr, A. L., Randall, R. J. (1951) J. Biol. Chem. 193, 265-275 [Free Full Text]
21. Strader, C. D., Candelore, M. R., Hill, W. S., Dixon, R. A. F., Sigal, I. S. (1989) J. Biol. Chem. 264, 16470-16477 [Abstract/Free Full Text]
22. Zhang, D., Weinstein, H. (1994) FEBS Lett. 337, 207-212 [CrossRef][Medline] [Order article via Infotrieve]
23. Brooks, R. R., Bruccoleri, R. E., Olafson, B. D., States, D. J., Swaminathan, S., Karplus, M. (1983) J. Comput. Chem. 4, 187-217
24. Gregoret, L. M., Rader, S. D., Fletterick, R. J., Cohen, F. E. (1991) Proteins 9, 99-107 [CrossRef][Medline] [Order article via Infotrieve]
25. Glennon, R. A., Wetkaemper, R. B., Bartyzel, P. (1991) Serotonin Receptor Subtypes: Basic and Clinical Aspects (Peroutka, S. J., eds) , p. 19, Wiley-Liss Inc., New York

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				G. P. Harris, V. M. Hapiak, R. T. Wragg, S. B. Miller, L. J. Hughes, R. J. Hobson, R. Steven, B. Bamber, and R. W. Komuniecki Three Distinct Amine Receptors Operating at Different Levels within the Locomotory Circuit Are Each Essential for the Serotonergic Modulation of Chemosensation in Caenorhabditis elegans J. Neurosci., February 4, 2009; 29(5): 1446 - 1456. [Abstract] [Full Text] [PDF]

				V. M. Hapiak, R. J. Hobson, L. Hughes, K. Smith, G. Harris, C. Condon, P. Komuniecki, and R. W. Komuniecki Dual Excitatory and Inhibitory Serotonergic Inputs Modulate Egg Laying in Caenorhabditis elegans Genetics, January 1, 2009; 181(1): 153 - 163. [Abstract] [Full Text] [PDF]

				R. T. Wragg, V. Hapiak, S. B. Miller, G. P. Harris, J. Gray, P. R. Komuniecki, and R. W. Komuniecki Tyramine and Octopamine Independently Inhibit Serotonin-Stimulated Aversive Behaviors in Caenorhabditis elegans through Two Novel Amine Receptors J. Neurosci., December 5, 2007; 27(49): 13402 - 13412. [Abstract] [Full Text] [PDF]

				M. C. Clark, T. E. Dever, J. J. Dever, P. Xu, V. Rehder, M. A. Sosa, and D. J. Baro Arthropod 5-HT2 Receptors: A Neurohormonal Receptor in Decapod Crustaceans That Displays Agonist Independent Activity Resulting from an Evolutionary Alteration to the DRY Motif J. Neurosci., March 31, 2004; 24(13): 3421 - 3435. [Abstract] [Full Text] [PDF]

				B. J. Ebersole, I. Visiers, H. Weinstein, and S. C. Sealfon Molecular Basis of Partial Agonism: Orientation of Indoleamine Ligands in the Binding Pocket of the Human Serotonin 5-HT2A Receptor Determines Relative Efficacy Mol. Pharmacol., January 1, 2003; 63(1): 36 - 43. [Abstract] [Full Text] [PDF]

				P. Manivet, B. Schneider, J. C. Smith, D.-S. Choi, L. Maroteaux, O. Kellermann, and J.-M. Launay The Serotonin Binding Site of Human and Murine 5-HT2B Receptors. MOLECULAR MODELING AND SITE-DIRECTED MUTAGENESIS J. Biol. Chem., May 3, 2002; 277(19): 17170 - 17178. [Abstract] [Full Text] [PDF]

				D. A. Shapiro, K. Kristiansen, D. M. Weiner, W. K. Kroeze, and B. L. Roth Evidence for a Model of Agonist-induced Activation of 5-Hydroxytryptamine 2A Serotonin Receptors That Involves the Disruption of a Strong Ionic Interaction between Helices 3 and 6 J. Biol. Chem., March 22, 2002; 277(13): 11441 - 11449. [Abstract] [Full Text] [PDF]

				J. A. Ballesteros, L. Shi, and J. A. Javitch Structural Mimicry in G Protein-Coupled Receptors: Implications of the High-Resolution Structure of Rhodopsin for Structure-Function Analysis of Rhodopsin-Like Receptors Mol. Pharmacol., July 1, 2001; 60(1): 1 - 19. [Abstract] [Full Text]

				I. Visiers, S. A. Hassan, and H. Weinstein Differences in conformational properties of the second intracellular loop (IL2) in 5HT2C receptors modified by RNA editing can account for G protein coupling efficiency Protein Eng. Des. Sel., June 1, 2001; 14(6): 409 - 414. [Abstract] [Full Text] [PDF]

				M. C. Gershengorn and R. Osman Minireview: Insights into G Protein-Coupled Receptor Function Using Molecular Models Endocrinology, January 1, 2001; 142(1): 2 - 10. [Abstract] [Full Text] [PDF]

				D. A. Shapiro, K. Kristiansen, W. K. Kroeze, and B. L. Roth Differential Modes of Agonist Binding to 5-Hydroxytryptamine2A Serotonin Receptors Revealed by Mutation and Molecular Modeling of Conserved Residues in Transmembrane Region 5 Mol. Pharmacol., November 1, 2000; 58(5): 877 - 886. [Abstract] [Full Text]

				K. Kristiansen, W. K. Kroeze, D. L. Willins, E. I. Gelber, J. E. Savage, R. A. Glennon, and B. L. Roth A Highly Conserved Aspartic Acid (Asp-155) Anchors the Terminal Amine Moiety of Tryptamines and Is Involved in Membrane Targeting of the 5-HT2A Serotonin Receptor But Does Not Participate in Activation via a "Salt-Bridge Disruption" Mechanism J. Pharmacol. Exp. Ther., June 1, 2000; 293(3): 735 - 746. [Abstract] [Full Text]

				S. Barroso, F. Richard, D. Nicolas-Etheve, J.-L. Reversat, J.-M. Bernassau, P. Kitabgi, and C. Labbe-Jullie Identification of Residues Involved in Neurotensin Binding and Modeling of the Agonist Binding Site in Neurotensin Receptor 1 J. Biol. Chem., January 7, 2000; 275(1): 328 - 336. [Abstract] [Full Text] [PDF]

				J. Sanders, Y. Oda, S. Roberts, A. Kiddie, T. Richards, J. Bolton, V. McGrath, S. Walters, D. Jaskolski, J. Furmaniak, et al. The Interaction of TSH Receptor Autoantibodies with 125I-Labelled TSH Receptor J. Clin. Endocrinol. Metab., October 1, 1999; 84(10): 3797 - 3802. [Abstract] [Full Text] [PDF]

				B. L. Roth, D. L. Willins, K. Kristiansen, and W. K. Kroeze Activation is Hallucinogenic and Antagonism is Therapeutic: Role of 5-HT2A Receptors in Atypical Antipsychotic Drug Actions Neuroscientist, July 1, 1999; 5(4): 254 - 262. [Abstract] [PDF]

				J. Ballesteros, S. Kitanovic, F. Guarnieri, P. Davies, B. J. Fromme, K. Konvicka, L. Chi, R. P. Millar, J. S. Davidson, H. Weinstein, et al. Functional Microdomains in G-protein-coupled Receptors. THE CONSERVED ARGININE-CAGE MOTIF IN THE GONADOTROPIN-RELEASING HORMONE RECEPTOR J. Biol. Chem., April 24, 1998; 273(17): 10445 - 10453. [Abstract] [Full Text] [PDF]

				M. Han, M. Groesbeek, T. P. Sakmar, and S. O. Smith The C9 methyl group of retinal interacts with glycine-121 in rhodopsin PNAS, December 9, 1997; 94(25): 13442 - 13447. [Abstract] [Full Text] [PDF]

				B. L. Roth, M. Shoham, M. S. Choudhary, and N. Khan Identification of Conserved Aromatic Residues Essential for Agonist Binding and Second Messenger Production at 5-Hydroxytryptamine2A Receptors Mol. Pharmacol., August 1, 1997; 52(2): 259 - 266. [Abstract] [Full Text]

				S. C. Sealfon, H. Weinstein, and R. P. Millar Molecular Mechanisms of Ligand Interaction with the Gonadotropin-Releasing Hormone Receptor Endocr. Rev., April 1, 1997; 18(2): 180 - 205. [Abstract] [Full Text]

				M. Han, S. W. Lin, S. O. Smith, and T. P. Sakmar The Effects of Amino Acid Replacements of Glycine 121on Transmembrane Helix 3of Rhodopsin J. Biol. Chem., December 13, 1996; 271(50): 32330 - 32336. [Abstract] [Full Text] [PDF]

				M. Han, S. W. Lin, M. Minkova, S. O. Smith, and T. P. Sakmar Functional Interaction of Transmembrane Helices 3and 6in Rhodopsin. REPLACEMENT OF PHENYLALANINE 261BY ALANINE CAUSES REVERSION OF PHENOTYPE OF A GLYCINE 121REPLACEMENT MUTANT J. Biol. Chem., December 13, 1996; 271(50): 32337 - 32342. [Abstract] [Full Text] [PDF]

				Y.-M. Sun, C. A. Flanagan, N. Illing, T. R. Ott, R. Sellar, B. J. Fromme, J. Hapgood, P. Sharp, S. C. Sealfon, and R. P. Millar A Chicken Gonadotropin-releasing Hormone Receptor That Confers Agonist Activity to Mammalian Antagonists. IDENTIFICATION OF D-LYS6 IN THE LIGAND AND EXTRACELLULAR LOOP TWO OF THE RECEPTOR AS DETERMINANTS J. Biol. Chem., March 9, 2001; 276(11): 7754 - 7761. [Abstract] [Full Text] [PDF]

				H. Frang, V. Cockcroft, T. Karskela, M. Scheinin, and A. Marjamaki Phenoxybenzamine Binding Reveals the Helical Orientation of the Third Transmembrane Domain of Adrenergic Receptors J. Biol. Chem., August 10, 2001; 276(33): 31279 - 31284. [Abstract] [Full Text] [PDF]

This Article Abstract Full Text (PDF) Submit a Letter to Editor Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Almaula, N. Articles by Sealfon, S. C. Search for Related Content PubMed PubMed Citation Articles by Almaula, N. Articles by Sealfon, S. C. Social Bookmarking                      What's this?