Limits...
Identification of critical residues in loop E in the 5-HT3ASR binding site.

Venkataraman P, Venkatachalan SP, Joshi PR, Muthalagi M, Schulte MK - BMC Biochem. (2002)

Bottom Line: Three tyrosine residues (Y140, Y142 and Y152) also significantly altered the binding of 5-HT3R ligands.Mutations in neighboring residues had little or no effect on binding of these ligands to the 5-HT3ASR.Our data also provides support for the hypothesis that this region of the receptor is present in a loop structure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurobiology, Northwestern University, Evanston, IL 60201. USA. padma964@hotmail.com

ABSTRACT

Background: The serotonin type 3 receptor (5-HT3R) 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-HT3ASR that correspond to the putative E binding loop of the nicotinic alpha7 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-HT3R antagonist [3H]granisetron. Three tyrosine residues (Y140, Y142 and Y152) also significantly altered the binding of 5-HT3R ligands. Mutations in neighboring residues had little or no effect on binding of these ligands to the 5-HT3ASR.

Conclusion: Our data supports a role for the putative E-loop region of the 5-HT3R 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.

Show MeSH
5-HT3R ligands.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC117120&req=5

Figure 1: 5-HT3R ligands.

Mentions: The purpose of this study is to extend the information available from other members of this receptor family to the 5-HT3R. Sequence homology and a presumed structural similarity to other ligand gated ion channels suggests that the E loop region of the 5-HT3AR forms part of the ligand binding domain for 5-HT3R ligands. This region extends from Y140 to K153 and is shown in Table 1. The homologous sequences of other representative members of this family are also shown. In the center of this region is a critical glycine residue that is thought to play a role in establishing a hairpin loop [12]. Recent x-ray crystallographic data obtained from an ACh binding protein (AChBP) shows a loop structure in this region resulting from a 3 residue turn containing a glycine homologous to G147 of the 5-HT3R. On either side of this putative turn region are residues that have been identified as important to receptor binding [12-18]. The formation of this loop structure brings amino acids on either side of glycine into close proximity and may form a binding pocket that will accommodate one or more functional groups. In order to identify the interaction of amino acids in this binding loop with 5-HT3R ligands, we have constructed alanine mutations of residues throughout this region and evaluated the alteration in binding affinity of 5 different classes of 5-HT3R ligands (Figure 1). Our data identifies 3 tyrosine residues that appear to interact selectively with each structural class and supports the existence of a loop structure in this region of the receptor.


Identification of critical residues in loop E in the 5-HT3ASR binding site.

Venkataraman P, Venkatachalan SP, Joshi PR, Muthalagi M, Schulte MK - BMC Biochem. (2002)

5-HT3R ligands.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC117120&req=5

Figure 1: 5-HT3R ligands.
Mentions: The purpose of this study is to extend the information available from other members of this receptor family to the 5-HT3R. Sequence homology and a presumed structural similarity to other ligand gated ion channels suggests that the E loop region of the 5-HT3AR forms part of the ligand binding domain for 5-HT3R ligands. This region extends from Y140 to K153 and is shown in Table 1. The homologous sequences of other representative members of this family are also shown. In the center of this region is a critical glycine residue that is thought to play a role in establishing a hairpin loop [12]. Recent x-ray crystallographic data obtained from an ACh binding protein (AChBP) shows a loop structure in this region resulting from a 3 residue turn containing a glycine homologous to G147 of the 5-HT3R. On either side of this putative turn region are residues that have been identified as important to receptor binding [12-18]. The formation of this loop structure brings amino acids on either side of glycine into close proximity and may form a binding pocket that will accommodate one or more functional groups. In order to identify the interaction of amino acids in this binding loop with 5-HT3R ligands, we have constructed alanine mutations of residues throughout this region and evaluated the alteration in binding affinity of 5 different classes of 5-HT3R ligands (Figure 1). Our data identifies 3 tyrosine residues that appear to interact selectively with each structural class and supports the existence of a loop structure in this region of the receptor.

Bottom Line: Three tyrosine residues (Y140, Y142 and Y152) also significantly altered the binding of 5-HT3R ligands.Mutations in neighboring residues had little or no effect on binding of these ligands to the 5-HT3ASR.Our data also provides support for the hypothesis that this region of the receptor is present in a loop structure.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Neurobiology, Northwestern University, Evanston, IL 60201. USA. padma964@hotmail.com

ABSTRACT

Background: The serotonin type 3 receptor (5-HT3R) 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-HT3ASR that correspond to the putative E binding loop of the nicotinic alpha7 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-HT3R antagonist [3H]granisetron. Three tyrosine residues (Y140, Y142 and Y152) also significantly altered the binding of 5-HT3R ligands. Mutations in neighboring residues had little or no effect on binding of these ligands to the 5-HT3ASR.

Conclusion: Our data supports a role for the putative E-loop region of the 5-HT3R 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.

Show MeSH