title: G-protein coupled receptors: SAR analyses of neurotransmitters and antagonists.
abstract: BACKGROUND
  From the deductive point of view, neurotransmitter receptors can be divided into categories such as cholinergic (muscarinic, nicotinic), adrenergic (alpha- and beta-), dopaminergic, serotoninergic (5-HT1 approximately 5-HT5), and histaminergic (H1 and H2). Selective agonists and antagonists of each receptor subtype can have specific useful therapeutic applications. For understanding the molecular mechanisms of action, an inductive method of analysis is useful.
  
  
  OBJECTIVE
  The aim of the present study is to examine the structure-activity relationships of agents acting on G-protein coupled receptors.
  
  
  METHODS
  Representative sets of G-PCR agonists and antagonists were identified from the literature and Medline [P.M. Walsh (2003) Physicians' Desk Reference; M.J. O'Neil (2001) The Merck Index]. The molecular weight (MW), calculated logarithm of octanol/water partition coefficient (C log P) and molar refraction (CMR), dipole moment (DM), E(lumo) (the energy of the lowest unoccupied molecular orbital, a measure of the electron affinity of a molecule and its reactivity as an electrophile), E(homo) (the energy of the highest occupied molecular orbital, related to the ionization potential of a molecule, and its reactivity as a nucleophile), and the total number of hydrogen bonds (H(b)) (donors and receptors), were chosen as molecular descriptors for SAR analyses.
  
  
  RESULTS
  The data suggest that not only do neurotransmitters share common structural features but their receptors belong to the same ensemble of G-protein coupled receptor with seven to eight transmembrane domains with their resultant dipoles in an antiparallel configuration. Moreover, the analysis indicates that the receptor exists in a dynamic equilibrium between the closed state and the open state. The energy needed to open the closed state is provided by the hydrolysis of GTP. A composite 3-D parameter frame setting of all the neurotransmitter agonists and antagonists are presented using MW, Hb and mu as independent variables.
  
  
  CONCLUSIONS
  It appears that all neurotransmitters examined in this study operate by a similar mechanism with the G-protein coupled receptors.
authors.affiliation: School of Pharmacy, University of Southern California, 1985 Zonal Avenue, Los Angeles, CA 90089-9121, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Kuo
authors.forename: R B
authors.initials: RB
authors.lastname: Wang
authors.forename: L J
authors.initials: LJ
authors.lastname: Shen
authors.forename: L L
authors.initials: LL
authors.lastname: Lien
authors.forename: E J
authors.initials: EJ
authors.lastname: Lien
mesh_terms: D000322:Adrenergic Agonists / Q000737:chemistry / Q000145:classification; D018674:Adrenergic Antagonists / Q000737:chemistry / Q000145:classification; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D018679:Cholinergic Agonists / Q000737:chemistry / Q000145:classification; D018680:Cholinergic Antagonists / Q000737:chemistry / Q000145:classification; D018491:Dopamine Agonists / Q000737:chemistry / Q000145:classification / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000737:chemistry / Q000145:classification / Q000494:pharmacology; D017442:Histamine Agonists / Q000737:chemistry / Q000145:classification / Q000494:pharmacology; D006633:Histamine Antagonists / Q000737:chemistry / Q000145:classification / Q000494:pharmacology; D008954:Models, Biological; D015394:Molecular Structure; D018377:Neurotransmitter Agents / Q000819:agonists / Q000037:antagonists & inhibitors* / Q000737:chemistry; D011941:Receptors, Adrenergic / Q000145:classification / Q000187:drug effects / Q000502:physiology; D011950:Receptors, Cholinergic / Q000145:classification / Q000187:drug effects / Q000502:physiology; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects* / Q000502:physiology*; D011968:Receptors, Histamine / Q000145:classification / Q000187:drug effects / Q000502:physiology; D012702:Serotonin Antagonists / Q000737:chemistry / Q000145:classification / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000737:chemistry / Q000145:classification / Q000494:pharmacology; D013329:Structure-Activity Relationship
chemical_list: D000322:Adrenergic Agonists; D018674:Adrenergic Antagonists; D018679:Cholinergic Agonists; D018680:Cholinergic Antagonists; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D017442:Histamine Agonists; D006633:Histamine Antagonists; D018377:Neurotransmitter Agents; D011941:Receptors, Adrenergic; D011950:Receptors, Cholinergic; D043562:Receptors, G-Protein-Coupled; D011968:Receptors, Histamine; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists