Figure 1: Overall view of the µ-OR structure
see the paper for essentially this exact figure.
Shown in is an overall view of the µ-opioid receptor bound to the morphinan antagonist (PDBid BF0). The seven parallel trans-membrane helices are the signature of a "TM7" cell membrane receptor, spanning the 35-40 nm distance across the lipid bilayer of the cell.
At the top we see three extracellular loops, EC1, EC2, and EC3. Below, we see a short helix that is inside the cell.
Notice that the inhibitor, shown as space-filling spheres, is nestled relatively deeply within the helical core. Binding at this position effects a change in conformation through a twisting action of the helices. This twisting gets delivered to a second binding site of the receptor on the endocellular (inside the cell) side. This second binding site is attached to the helical assembly via TM3 and TM6 (not shown here). It is where an associated protein that binds GTP can bind. This protein's binding is what makes this receptor a "G-protein-coupled receptor." Its binding triggers the transmission of the chemical "signal" delivered by the opioid (or, in this case, being prevented from doing that).
Investigate the structure after loading the by dragging it around using your mouse or clicking the buttons below. SHIFT-drag to zoom.
