Once you remove the scorpion toxin (yellow) you can see that the potassium channel (primarily green) is a 4-subunit transmembrane protein that allows rapid passage of potassium ions – but not sodium ions – across the membrane. Four subunits form the channel. You’ll see carbonyl oxygen atoms precisely positioned to replace the water that normally hydrates each potassium ion. Since there is no energetic difference between a hydrated potassium ion and the same ion bound in the pore of the channel, the ion rapidly passes through in a frictionless manner.
The yellow scorpion toxin section of the model is based on the Chinese scorpion Buthus martensi. It is a long chain peptide with 66 amino acid residues, including 8 cysteines that form 4 disulfide bonds. You will see that the cysteines forming disulfide bonds are shown on the model and are colored yellow and gray. The cysteines and resulting disulfide bonds are important in the folding and stabilizing of the scorpion toxin.
Positive lysine (41) interacts with the negative oxygen at the entrance to the channel and effectively blocks potassium from passing through. The model also displays selected amino acid side chains that are important in stabilizing the interaction between these 2 proteins.
The potassium channel is important in regulation and a wide variety of processes including cell excitability and proliferation, heartbeat regulation, muscle contraction, neurotransmission, insulin secretion and signal transduction. Much of the knowledge of the function of potassium channels has been gained using scorpion toxins. Most of the toxins that bind to the potassium channels are short peptides consisting of 28 to 40 amino acids.
While there are more than 2,000 species of scorpions, only 30 – 40 have enough toxin to kill a person. Other peptides in scorpion venom can bind to sodium, chloride or calcium channels.
This model is made of plaster by rapid prototyping and should be handled with care. It will break if dropped, held tightly or handled roughly.