Antagonists of the receptor-G protein interface block Gi-coupled signal transduction.
The carboxyl terminus of heterotrimeric G protein alpha subunits plays an important role in receptor interaction. We demonstrate that peptides corresponding to the last 11 residues of Galphai1/2 or Galphao1 impair agonist binding to A1 adenosine receptors, whereas Galphas or Galphat peptides have no effect. Previously, by using a combinatorial library we identified a series of Galphat peptide analogs that bind rhodopsin with high affinity (Martin, E. L., Rens-Domiano, S., Schatz, P. J., and Hamm, H. E. (1996) J. Biol. Chem. 271, 361-366). Native Galphai1/2 peptide as well as several analogs were tested for their ability to modulate agonist binding or antagonist-agonist competition using cells overexpressing human A1 adenosine receptors. Three peptide analogs decreased the Ki, suggesting that they disrupt the high affinity receptor-G protein interaction and stabilize an intermediate affinity state. To study the ability of the peptides to compete with endogenous Galphai proteins and block signal transduction in a native setting, we measured activation of G protein-coupled K+ channels through A1 adenosine or gamma-aminobutyric acid, type B, receptors in hippocampal CA1 pyramidal neurons. Native Galphai1/2, peptide, and certain analog peptides inhibited receptor-mediated K+ channel gating, dependent on which receptor was activated. This differential perturbation of receptor-G protein interaction suggests that receptors that act on the same G protein can be selectively disrupted.
Gilchrist
A
A
Department of Pharmacology, University of Illinois, Chicago, Illinois 60612, USA.
Mazzoni
M R
MR
Dineen
B
B
Dice
A
A
Linden
J
J
Proctor
W R
WR
Lupica
C R
CR
Dunwiddie
T V
TV
Hamm
H E
HE
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001667:Binding, Competitive / Q000502:physiology; D001921:Brain / Q000378:metabolism; D002478:Cells, Cultured; D004594:Electrophysiology; D019204:GTP-Binding Proteins / Q000737:chemistry*; D006801:Humans; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018079:Receptors, GABA / Q000502:physiology; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D012243:Rhodopsin / Q000031:analogs & derivatives / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D014970:Xanthines / Q000378:metabolism
D010446:Peptide Fragments; D018079:Receptors, GABA; D018047:Receptors, Purinergic P1; D014970:Xanthines; C047235:N-(1-methyl-2-phenylethyl)adenosine; C013110:metarhodopsins; D012243:Rhodopsin; C051360:1,3-dipropyl-8-cyclopentylxanthine; D019204:GTP-Binding Proteins; D001418:Baclofen; D000241:Adenosine