TY - JOUR
T1 - Contribution of a helix 5 locus to selectivity of hallucinogenic and nonhallucinogenic ligands for the human 5-hydroxytryptamine(2A) and 5- hydroxytryptamine(2C) receptors
T2 - Direct and indirect effects on ligand affinity mediated by the same locus
AU - Almaula, Niva
AU - Ebersole, Barbara J.
AU - Ballesteros, Juan A.
AU - Weinstein, Harel
AU - Sealfon, Stuart C.
PY - 1996/7
Y1 - 1996/7
N2 - An important determinant of the neurobehavioral responses induced by a drug is its relative receptor selectivity. The molecular basis of ligand selectivity of hallucinogenic and nonhallucinogenic compounds of varying structural classes for the human 5-hydroxytryptamine (5-HT)(2A) and 5-HT(2C) receptors was investigated with the use of reciprocal site-directed mutagenesis. Because these two closely related receptor subtypes differ in the amino acid present at position 5.46 (residues 242 and 222 in the sequences, respectively), the effects of corresponding substitutions in the 5-HT(2A) [S5.46(242) → A] and 5-HT(2C) [A5.46(222) → S] receptors were studied in tandem. By studying both receptors, the direct and indirect effects of mutations on affinity and selectivity can be distinguished. The ergolines studied, mesulergine (selective for the 5-HT(2C) receptor) and d- lysergic acid diethylamide (selective for the 5-HT(2A) receptor), reversed their relative affinity with mutations in each receptor, supporting a direct role of this locus in the selectivity of these ligands. However, interchange mutations in either receptor led to decreased or unchanged affinity for (±)- 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane and ketanserin, which have higher affinity for the 5-HT(2A) receptor, consistent with little contribution of this locus to the selectivity of these ligands. The indoleamines studied were affected differently by mutations in each receptor, suggesting that they bind differently to the two receptor subtypes. Mutation of this locus in the 5-HT(2A) receptor decreased the affinity of all indoleamines, whereas the interchange mutation of the 5-HT(2C) receptor did not affect indoleamine affinity. These results are consistent with a direct interaction between this side chain and indoleamines for the 5-HT(2A) receptor but not for the 5-HT(2C) receptor. Furthermore, this analysis shows that the higher affinity of 5-HT and tryptamine for the 5-HT(2C) receptor than for the 5-HT(2A) receptor is not due to the difference at this locus. The hallucinogens studied [d-lysergic acid diethylamide, psilocin, bufotenin, and (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane] fell into different classes in this analysis. For the classes of ligand studied, the side-chain difference at this position directly determines relative ligand selectivity only for ergolines and may contribute to the specific effects of hallucinogens in this class.
AB - An important determinant of the neurobehavioral responses induced by a drug is its relative receptor selectivity. The molecular basis of ligand selectivity of hallucinogenic and nonhallucinogenic compounds of varying structural classes for the human 5-hydroxytryptamine (5-HT)(2A) and 5-HT(2C) receptors was investigated with the use of reciprocal site-directed mutagenesis. Because these two closely related receptor subtypes differ in the amino acid present at position 5.46 (residues 242 and 222 in the sequences, respectively), the effects of corresponding substitutions in the 5-HT(2A) [S5.46(242) → A] and 5-HT(2C) [A5.46(222) → S] receptors were studied in tandem. By studying both receptors, the direct and indirect effects of mutations on affinity and selectivity can be distinguished. The ergolines studied, mesulergine (selective for the 5-HT(2C) receptor) and d- lysergic acid diethylamide (selective for the 5-HT(2A) receptor), reversed their relative affinity with mutations in each receptor, supporting a direct role of this locus in the selectivity of these ligands. However, interchange mutations in either receptor led to decreased or unchanged affinity for (±)- 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane and ketanserin, which have higher affinity for the 5-HT(2A) receptor, consistent with little contribution of this locus to the selectivity of these ligands. The indoleamines studied were affected differently by mutations in each receptor, suggesting that they bind differently to the two receptor subtypes. Mutation of this locus in the 5-HT(2A) receptor decreased the affinity of all indoleamines, whereas the interchange mutation of the 5-HT(2C) receptor did not affect indoleamine affinity. These results are consistent with a direct interaction between this side chain and indoleamines for the 5-HT(2A) receptor but not for the 5-HT(2C) receptor. Furthermore, this analysis shows that the higher affinity of 5-HT and tryptamine for the 5-HT(2C) receptor than for the 5-HT(2A) receptor is not due to the difference at this locus. The hallucinogens studied [d-lysergic acid diethylamide, psilocin, bufotenin, and (±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane] fell into different classes in this analysis. For the classes of ligand studied, the side-chain difference at this position directly determines relative ligand selectivity only for ergolines and may contribute to the specific effects of hallucinogens in this class.
UR - https://www.scopus.com/pages/publications/0030014571
U2 - 10.1016/s0026-895x(25)09149-7
DO - 10.1016/s0026-895x(25)09149-7
M3 - Article
C2 - 8700116
AN - SCOPUS:0030014571
SN - 0026-895X
VL - 50
SP - 34
EP - 42
JO - Molecular Pharmacology
JF - Molecular Pharmacology
IS - 1
ER -