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