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G Proteins

Exploring the Structure

G proteins use GTP to switch to their active state. In the active form, shown on the right from PDB entry 1gia, the last phosphate group in GTP contacts a short loop on the surface of the protein, holding it tightly against the surface. The GTP is shown with spheres, and the loop is colored red. When GTP is cleaved into GDP, however, this phosphate group is removed, and the shorter GDP molecule cannot contact the loop. This allows a looser structure in the loop, which is recognized in the inactive trimeric complex, as shown on the left in PDB entry 1gg2.

Also, be sure to spend some time looking at the beta subunit, for instance, in PDB entries 1gg2, 1got or 1tbg. If you draw a chain trace or a ribbon diagram, you will see that the chain folds into a beautiful propeller-shaped structure.

These illustrations were created with RasMol. You can create similar pictures by clicking on the accession codes and picking one of the options under View Structure. For more information on G proteins, click here.

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