Untitled

Abstract

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.

The binding orientations of structurally-related ligands can differ; A cautionary note

“…As a similar side chain orientation is seen in 4PIR, ligand interactions with this residue are also likely in the 5-HT 3 receptor binding site and are supported by the large effects we see for both ligands ( Kesters et al., 2013 ). Substitution of another aromatic residue, W90 in loop D, also abolished the binding of both tropisetron and granisetron, similar to reports for other 5-HT 3 receptor ligands ( Thompson et al., 2014 , Venkataraman et al., 2002 , Yan et al., 1999 ). Again, the aromatic character of W90 is important as removal of the aromatic ring (W90A, W90S) eliminates granisetron binding, but conservative substitutions (W90Y) have reduced effects ( Price and Lummis, 2004 , Spier and Lummis, 2000 , Thompson et al., 2005 , Yan and White, 2005 ).…”

Further Studies on the Interaction of the 5-Hydroxytryptamine3(5-HT3) Receptor with Arylpiperazine Ligands. Development of a New 5-HT3Receptor Ligand Showing Potent Acetylcholinesterase Inhibitory Properties

“…However, in both cases the proposed binding cleft for antagonist ligands is similar, being composed of a vestibule where residue Glu236(171) (the first number corresponds to the whole sequence from rat 5HT 3 R; the number in parentheses corresponds to the portion of the sequence modeled in ref ) lies, whereas the back of the cavity is composed of hydrophobic residues such as Trp90(25) and Tyr234(169). Recent results from site-directed mutagenesis studies confirmed the outstanding importance of these residues − in the ligand binding interaction, thus supporting the predictive value of the modeling procedures. To verify the receptor capability of accommodating bivalent ligands and possibly to identify the putative additional binding pocket, the 6o ligand was docked into an updated three-dimensional model obtained by means of the alignment recently reported by Maksay et al…”

The binding characteristics and orientation of a novel radioligand with distinct properties at 5-HT3A and 5-HT3AB receptors

“…The effects of this second site are apparent at concentrations of [ 3 H]VUF10166 > 3 nM, and are consistent with previous work that identified an additional allosteric binding site for unlabelled VUF10166 at the A+B− interface ( Thompson et al., 2012 ). Docking of this competitive ligand into the orthosteric (A+A−) binding site, combined with data from mutagenesis, suggest that VUF10166 is oriented with its quinoxaline rings close to W183 and its basic nitrogen extended towards loop E. Individual residues, many of which have been previously shown to be important in studies of other 5-HT 3 receptor ligands (including d -tubocurarine, granisetron, lerisetron, meta -chlorophenylbiguanide and tropisetron) are also important for VUF10166 binding ( Hope et al., 1999; Mochizuki et al., 1999; Venkataraman et al., 2002a; Price and Lummis, 2004 ). The residues are discussed in more detail below.…”

“…In 5HTBP the equivalent residue (W53) is involved in van der Waals interactions with granisetron and W90 may have a similar role in binding VUF10166 ( Spier and Lummis, 2000; Price and Lummis, 2004; Thompson et al., 2005; Yan and White, 2005 ). Substitutions at W90 decrease the affinity of other potent 5-HT 3 receptor-specific ligands such as curare, lerisetron and 5-HT ( Yan et al., 1999; Venkataraman et al., 2002a ) R92 interacts with granisetron in 5HTBP (R55), and the effects of its substitution on the affinity of VUF10166, ondansetron, granisetron and MDL72222, suggest an interaction with all of these ligands ( Thompson et al., 2005; Yan and White, 2005 ).…”