title: Allosteric modulation of dopamine D2 receptors by homocysteine.
abstract: It has been suggested that L-DOPA-induced hyperhomocysteinemia can increase the risk of stroke, heart disease, and dementia and is an additional pathogenetic factor involved in the progression of Parkinson's disease. In Chinese hamster ovary (CHO) cells stably cotransfected with adenosine A(2A) and dopamine D2 receptors, homocysteine selectively decreased the ability of D2 receptor stimulation to internalize adenosine A(2A)-dopamine D2 receptor complexes. Radioligand-binding experiments in the same cell line demonstrated that homocysteine acts as an allosteric D2 receptor antagonist, by selectively reducing the affinity of D2 receptors for agonists but not for antagonists. Mass spectrometric analysis showed that, by means of an arginine (Arg)-thiol electrostatic interaction, homocysteine forms noncovalent complexes with the two Arg-rich epitopes of the third intracellular loop of the D2 receptor, one of them involved in A(2A)-D2 receptor heteromerization. However, homocysteine was unable to prevent or disrupt A(2A)-D2 receptor heteromerization, as demonstrated with Fluorescence Resonance Energy Transfer (FRET) experiments in stably cotransfected HEK cells. The present results could have implications for Parkinson's disease.
authors.affiliation: Department of Biomedical Sciences, University of Modena, 41100 Modena, Italy. luigiagnati@tin.it
authors.forename: Luigi F
authors.initials: LF
authors.lastname: Agnati
authors.forename: Sergi
authors.initials: S
authors.lastname: Ferré
authors.forename: Susanna
authors.initials: S
authors.lastname: Genedani
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Leo
authors.forename: Diego
authors.initials: D
authors.lastname: Guidolin
authors.forename: Monica
authors.initials: M
authors.lastname: Filaferro
authors.forename: Paulina
authors.initials: P
authors.lastname: Carriba
authors.forename: Vicent
authors.initials: V
authors.lastname: Casadó
authors.forename: Carme
authors.initials: C
authors.lastname: Lluis
authors.forename: Rafael
authors.initials: R
authors.lastname: Franco
authors.forename: Amina S
authors.initials: AS
authors.lastname: Woods
authors.forename: Kjell
authors.initials: K
authors.lastname: Fuxe
mesh_terms: D000494:Allosteric Regulation / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D000939:Epitopes / Q000032:analysis / Q000737:chemistry; D006710:Homocysteine / Q000494:pharmacology*; D006801:Humans; D010446:Peptide Fragments / Q000737:chemistry; D011869:Radioligand Assay; D017448:Receptors, Dopamine D2 / Q000737:chemistry / Q000187:drug effects / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000187:drug effects; D014162:Transfection
chemical_list: D000939:Epitopes; D010446:Peptide Fragments; D017448:Receptors, Dopamine D2; D011994:Recombinant Proteins; D006710:Homocysteine