The signal transfer regions of G alpha(s).
The crystal structure of soluble functional fragments of adenylyl cyclase complexed with G alpha(s) and forskolin, shows three regions of G alpha(s) in direct contact with adenylyl cyclase. The functions of these three regions are not known. We tested synthetic peptides encoding these regions of G alpha(s) on the activities of full-length adenylyl cyclases 2 and 6. A peptide encoding the Switch II region (amino acids 222-247) stimulated both adenylyl cyclases 2- to 3-fold. Forskolin synergized the stimulation. Addition of peptides in the presence of activated G alpha(s) partially inhibited G alpha(s) stimulation. Corresponding Switch II region peptides from G alpha(q) and G alpha(i) did not stimulate adenylyl cyclase. A peptide encoding the Switch I region (amino acids 199-216) also stimulated AC2 and AC6. The stimulatory effects of the two peptides at saturating concentrations were non-additive. A peptide encoding the third contact region (amino acids 268-286) located in the alpha 3-beta 5 region, inhibits basal, forskolin, and G alpha(s)-stimulated enzymatic activities. Since this region in G alpha(s) interacts with both the central cytoplasmic loop and C-terminal tail of adenylyl cyclases this peptide may be involved in blocking interactions between these two domains. These functional data in conjunction with the available structural information suggest that G alpha(s) activation of adenylyl cyclase is a complex event where the alpha 3-beta 5 loop of G alpha(s) may bring together the central cytoplasmic loop and C-terminal tail of adenylyl cyclase thus allowing the Switch I and Switch II regions to function as signal transfer regions to activate adenylyl cyclase.
Chen
Y
Y
Department of Pharmacology, Mount Sinai School of Medicine, New York, New York 10029, USA.
Yoo
B
B
Lee
J B
JB
Weng
G
G
Iyengar
R
R
D000262:Adenylyl Cyclases / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D004789:Enzyme Activation; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D010446:Peptide Fragments; D015398:Signal Transduction
D010446:Peptide Fragments; D005576:Colforsin; D020962:Heterotrimeric GTP-Binding Proteins; D000262:Adenylyl Cyclases