title: Biarsenical ligands bind to endogenous G-protein α-subunits and enable allosteric sensing of nucleotide binding.
abstract: BACKGROUND
  Heterotrimeric G-proteins relay extracellular signals to intracellular effector proteins. Multiple methods have been developed to monitor their activity; including labeled nucleotides and biosensors based on genetically engineered G-proteins. Here we describe a method for monitoring unlabeled nucleotide binding to endogenous G-proteins α-subunits in a homogeneous assay based on the interaction of 4',5'-bis(1,2,3-dithioarsolan-2-yl)-2',7'-difluorofluorescein (F2FlAsH) with G-protein α-subunits.
  
  
  RESULTS
  The biarsenic fluorescent ligand F2FlAsH binds to various wild-type G-protein α-subunits (αi1, αi2, αi3, αslong, αsshort, αolf, αq, α13) via high affinity As-cysteine interactions. This allosteric label enables real time monitoring of the nucleotide bound states of α-subunits via changes in fluorescence anisotropy and intensity of their F2FlAsH-complexes. We have found that different α-subunits displayed different signal amplitudes when interacting with F2FlAsH, being more sensitive to nucleotide binding to αi, αs, αolf and αq than to α13. Addition of nucleotides to F2FlAsH-labeled α-subunits caused concentration-dependent effects on their fluorescence anisotropy. pEC50 values of studied nucleotides depended on the subtype of the α-subunit and were from 5.7 to 8.2 for GTPγS, from 5.4 to 8.1 for GppNHp and from 4.8 to 8.2 for GDP and lastly up to 5.9 for GMP. While GDP and GMP increased the fluorescence anisotropy of F2FlAsH complexes with αi-subunits, they had the opposite effect on the other αβγM complexes studied.
  
  
  CONCLUSIONS
  Biarsenical ligands interact allosterically with endogenous G-protein α-subunits in a nucleotide-sensitive manner, so the presence or absence of guanine nucleotides has an effect on the fluorescence anisotropy, intensity and lifetime of F2FlAsH-G-protein complexes.
authors.forename: Lauri
authors.initials: L
authors.lastname: Tõntson
authors.forename: Sergei
authors.initials: S
authors.lastname: Kopanchuk
authors.affiliation: University of Tartu, Institute of Chemistry, Ravila 14a, 50411, Tartu, Estonia. ago.rinken@ut.ee.
authors.forename: Ago
authors.initials: A
authors.lastname: Rinken
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001152:Arsenicals / Q000737:chemistry / Q000378:metabolism*; D003545:Cysteine / Q000737:chemistry / Q000378:metabolism; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000737:chemistry / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006157:Guanosine Monophosphate / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D009711:Nucleotides / Q000378:metabolism*; D011485:Protein Binding; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D061987:Sf9 Cells; D018411:Spodoptera
chemical_list: D001152:Arsenicals; D005456:Fluorescent Dyes; D044385:GTP-Binding Protein alpha Subunits; D008024:Ligands; D009711:Nucleotides; D011994:Recombinant Proteins; D006157:Guanosine Monophosphate; D003545:Cysteine