Molecule of the Month: G Proteins
G proteins receive signals from cellular receptors and deliver them inside the cell
Reading the Mail
The "G" in G Proteins
Hugging the Membrane
G Proteins Under Attack
Relaying the Signal
One major advantage of this approach is that it allows the signal to be amplified. In the signaling chain shown here, a single molecule of adrenaline can stimulate the production of many molecules of cyclic AMP. By incorporating an enzyme (like adenylyl cyclase) into the chain, a weak signal from outside the cell can be translated into a strong signal throughout the inside of the cell.
Exploring the Structure
G-proteins in Action
These two structures show how G proteins use GTP to switch to their active state. PDB entry 6eg8 is the inactive state with GDP bound. The two phosphates are shown in green here, and the signalling helix is shown in red. PDB entry 1cjk is the active form with GTP bound (notice that it is longer than the GDP), which pushes the signaling helix into a different conformation that is perfect for binding to adenylyl cyclase. This structure has an analog of ATP bound in the active site of adenylyl cyclase, and forskolin, a plant molecule that activates the enzyme, bound in a neighboring site. Click on the image to explore these structures interactively in Jmol. While you're doing that, be sure to try the cartoon representation to see the beautifully-symmetric propeller-shaped fold of the beta subunit in the inactive structure.
Topics for Further Discussion
- Try searching for "cyclic AMP" to see structures of many of the proteins that are regulated by cAMP.
- You can explore the structure of cyclic AMP in the Chemical Component Library for CMP.
Related PDB-101 Resources
- Browse Cellular Signaling
- Browse Toxins and Poisons
- Browse Nobel Prizes and PDB structures
- Browse Drugs and the Brain
- 6eg8: Liu, X., Xu, X., Hilger, D., Aschauer, P., Tiemann, J.K.S., Du, Y., Liu, H., Hirata, K., Sun, X., Guixa-Gonzalez, R., Mathiesen, J.M., Hildebrand, P.W., Kobilka, B.K. (2019) Structural Insights into the Process of GPCR-G Protein Complex Formation. Cell 177: 1243-1251.e12
- 6r3q: Qi, C., Sorrentino, S., Medalia, O., Korkhov, V.M. (2019) The structure of a membrane adenylyl cyclase bound to an activated stimulatory G protein. Science 364: 389-394
- 3sn6: Rasmussen, S.G., DeVree, B.T., Zou, Y., Kruse, A.C., Chung, K.Y., Kobilka, T.S., Thian, F.S., Chae, P.S., Pardon, E., Calinski, D., Mathiesen, J.M., Shah, S.T., Lyons, J.A., Caffrey, M., Gellman, S.H., Steyaert, J., Skiniotis, G., Weis, W.I., Sunahara, R.K., Kobilka, B.K. (2011) Crystal structure of the beta2 adrenergic receptor-Gs protein complex Nature 477: 549-555
- 1cjk: Tesmer, J.J., Sunahara, R.K., Johnson, R.A., Gosselin, G., Gilman, A.G., Sprang, S.R. (1999) Two-metal-Ion catalysis in adenylyl cyclase. Science 285: 756-760
- Sprang, S.R. (1997) G protein mechanisms: insights from structural analysis. Annual Review of Biochemistry 66, 639-678.
- Bourne, H.R. (1997) How receptors talk to trimeric G proteins. Current Opinion in Cell Biology 9, 134-142.
- Coleman, D.E., Sprang, S.R. (1996) How G proteins work. Trends in Biochemical Sciences 21, 41-44.
- 1tbg: Sondek, J., Bohm, A., Lambright, D.G., Hamm, H.E., Sigler, P.B.(1996) Crystal structure of a G-protein beta gamma dimer at 2.1A resolution. Nature 379: 369-374
- Hepler, J.R., Gilman, A.G. (1992) G proteins. Trends in Biochemical Sciences 17, 383-387.
- Linder, M.E., Gilman, A.G. (1992) G proteins. Scientific American 267(1), 56-65.
October 2004, David Goodsell, updated September 2020doi:10.2210/rcsb_pdb/mom_2004_10