title: Alkylation of sulfhydryl groups on Galpha(s/olf) subunits by N-ethylmaleimide: regulation by guanine nucleotides.
abstract: In rat striatum A(2A) adenosine receptors activate adenylyl cyclase through coupling to G(s)-like proteins, mainly G(olf) that is expressed at high levels in this brain region. In this study we report that the sulfhydryl alkylating reagent, N-ethylmaleimide (NEM), causes a concentration- and time-dependent inhibition of [3H] 2-p-(2-carboxyethyl)phenylethylamino)-5'-N-ethylcarboxamido adenosine ([3H]CGS21680) binding to rat striatal membranes. Membrane treatment with [14C]N-ethylmaleimide ([14C]NEM) labels numerous proteins while addition of 5'-guanylylimidodiphosphate (Gpp(NH)p) reduces labeling of only three protein bands that migrate in SDS-polyacrylamide gel electrophoresis with apparent molecular masses of approximately 52, 45 and 39 kDa, respectively. The 52- and 45-kDa labeled bands show electrophoretic motilities as Galpha(s)-long and Galpha(s)-short/Galpha(olf) subunits. An anti-Galpha(s/olf) antiserum immunoprecipitates two 14C labeled bands of 44 and 39 kDa. The band density decreases by 21-26% when membranes are treated with NEM in the presence of Gpp(NH)p. An anti-A(2A) receptor antibody also immunoprecipitates two 14C labeled bands of 40 and 38 kDa, respectively. However, such protein bands do not show any decrease of their density upon membrane treatment with NEM plus Gpp(NH)p. These results indicate that in rat striatal membranes NEM alkylates sulfhydryl groups of both Galpha(s/olf) subunits and A(2A) adenosine receptors. In addition, cysteine residues of Galpha(s/olf) are easily accessible to modification when the subunit is in the GDP-bound form. The 39- and 38-kDa labeled proteins may represent proteolytic fragments of Galpha(s/olf) and A(2A) adenosine receptor, respectively.
authors.affiliation: Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, Sezione di Neurobiologia e Famacologia, Via Bonanno 6, 56126 Pisa, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Giusti
authors.forename: Simone
authors.initials: S
authors.lastname: Taddei
authors.forename: Francesca
authors.initials: F
authors.lastname: Ceccarelli
authors.forename: Silvio
authors.initials: S
authors.lastname: Chericoni
authors.forename: Gianni
authors.initials: G
authors.lastname: Bigini
authors.forename: Antonio
authors.initials: A
authors.lastname: Lucacchini
authors.forename: Maria R
authors.initials: MR
authors.lastname: Mazzoni
mesh_terms: D000478:Alkylation; D000818:Animals; D001921:Brain / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology*; D044385:GTP-Binding Protein alpha Subunits; D006150:Guanine Nucleotides / Q000378:metabolism*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000502:physiology; D013438:Sulfhydryl Compounds / Q000494:pharmacology
chemical_list: D044385:GTP-Binding Protein alpha Subunits; D006150:Guanine Nucleotides; D021122:Protein Subunits; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1; D013438:Sulfhydryl Compounds; C084618:olfactory G protein subunit alpha olf; D006165:Guanylyl Imidodiphosphate; D020962:Heterotrimeric GTP-Binding Proteins; D005033:Ethylmaleimide