Build a Paper Model of a G Protein-Coupled Receptor (GPCR)

Build a Paper Model of a G Protein-Coupled Receptor (GPCR)


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.