G protein-coupled receptors or GPCRs for short are a large family of membrane-embedded receptors,
with structural features that have been preserved through the course of evolution. This model
represents the shared architectural traits of GPCRs. With the extracellular N-terminus,
the protein chain folds to form a bundle of seven transmembrane alpha helices
connected by 3 intracellular and 3 extracellular loops
with the C-terminus reaching inside the cell.
On the extracellular side, the helices form a cavity where ligands such as endorphins,
morphine or serotonin bind. On the intracellular side, the receptor is coupled to G-protein.
When the receptor is activated by a ligand, the G protein splits in two parts which then
activate other proteins in the internal signal transduction pathways.
To create this model, you will need to download and print the template from PDB-101. You will
also need scissors and tape.
In this model, the dotted lines are for cutting and the solid black lines for folding.
The dark gray and the semi-transparent gray areas will be hidden in the final model.
Cut the 7 paddle-shaped pieces along the dotted lines.
Create the alpha helices numbered 1-7. For each helix, fold along the solid lines to create a triangular prism.
Hide the dark gray flap inside.
The tail ends of the paddles will represent loops in the final model. Connect each loop
with the next helix by matching and taping lower-case letters a through f.
Now, by following the thick blue line, you can see how the full polymer chain folds into alpha helices.
Connect helices 1 and 2 by aligning the semi-transparent gray area marked 1B with the semi-transparent
gray area marked 2A, matching the position of the diamond symbols and taping them together.
Notice the first intracellular loop forming.
Connect helices 2 and 3 by aligning the areas 2B and 3A, matching the position of the circles.
Now you will notice the first extracellular loop forming.
In many GPCRs, the 7-helix bundle is not perfectly symmetrical,
and helix 4 is found towardsthe outside of the bundle.
Form the intracellular loop between helix 3 and the extracellular one between helices 4 and 5 but let the helix 4 dangle on the side.
Connect helices 3 and 5 by aligning area 3B to 5A,
matching the position of the symbol with 4 diamonds.
Connect helices 5 and 6 by aligning areas 5B and 6A, matching the position of the raindrop symbols.
Now you will notice the last intracellular loop forming.
Connect helices 6 and 7 by aligning areas 6B and 7A, matching the position of the flower symbols.
Now you will notice the last extracellular loop forming.
Finish the model by taping together helix 7 and 1. Be sure to align the semitransparent
gray area between 7B and 1A and match the position of the sun symbol.
Now you will notice the cavity at the top that represents the ligand binding site.