King Kong toxin, a component of the venom in some poisonous marine snails, has a peculiar power to go with its peculiar name.
When injected into a meek little lobster in a tank full of superiors, the poison induces delusions of grandeur; the little guy starts marching around like he's king of the tank. Any given venom can contain hundreds of toxins such as King Kong, including some that are medically useful, but teasing them out of a venom sample is no mean feat. Now, in a methodological breakthrough, researchers at The Rockefeller University have devised a method to speed up this distillation process by orders of magnitude, raising the prospect that they will be able to test a great many of these molecules for their medical potential.
Odd as it may sound, some of the deadliest natural agents in the world have the potential to become among the most beneficial, because their array of peptide components - or toxins - has been refined over hundreds of millions of years of evolution to exquisitely target and manipulate different kinds of cells. "These little creatures that inhabit our planet are masters of developing these bioactive molecules far, far, better than we are," says Brian T. Chait, head of the Laboratory of Mass Spectrometry and Gaseous Ion Chemistry at Rockefeller, where the research was conducted. "It's a huge, largely untapped treasure of beautiful molecules."
The challenge is to break down the tremendously complex venom toxins into their constituent peptides, and then further to identify the exact amino acid sequence of each peptide, so that they can be precisely replicated and tested to discover exactly what they're so good at.
Chait, postdoctoral associate Beatrix Ueberheide, senior research associate David Fenyo and Paul Alewood at the University of Queensland focused on the venom from a single cone snail, a member of Conus textile known as "cloth of gold" for its brilliant shell. "It's a very slow, rather beautiful snail that creeps along and hunts other molluscs," says Chait. "Closely related cone snails hunt fish, and since fish can move in three dimensions very fast, the snails must kill very quickly," Chait says. Their powerful venom, which has killed several humans as well, is shot through a harpoon-like needle that the snail thrusts into the fish. "It's like a lightning strike," says Ueberheide.
Historically, the mission to decode the cone snail's venom peptides has unfortunately proceeded at a snail's pace, with research teams sometimes taking a good portion of a year to find the cipher for a single one. The new method developed at Rockefeller can ratchet that rate by orders of magnitude.
In research published this month by the Proceedings of the National Academy of Sciences , the team revealed the complete amino acid sequence, also known as the de novo sequence, of 31 of the cone snail's peptides, including King Kong toxin, using less than seven percent of their subject's venom. "Until recently, sequencing even a single toxin often required pooling the venom from a number of snails," Chait says.
The practice of mass spectrometry distills the elemental amino acid sequences of peptides that make up proteins by cutting the bonds among amino acids, ideally between each one, and measuring the resulting particles' mass-to-charge ratio. That data is then compared against the mass-to-charge ratios of known amino acid sequences. But the data often has gaps because the mass spectrometer cannot break the bonds in all of the right places, and some of the particles are not charged and so cannot be measured.
The Rockefeller team devised a way to charge up the toxin samples, allowing the mass spectrometer to cut more peptide bonds using the relatively new technique of electron transfer dissociation (ETD). The result was data having much higher information content and containing fewer of the gaps that slow down researchers using traditional techniques. The team also developed a computer program that helps fill in the gaps by checking partial sequences against a database containing the DNA code for known venom peptides.
Certain individual peptide toxins are known to very specifically target just a single type of ion channel. In the cone snail, which must kill instantly to capture its prey, the complex venom mixture targets a broad array of different ion channels that control motor movement and neurological transmission. The team hopes eventually to decode large numbers of venom peptides and determine their targets. "Ultimately, we want to have a vast panel of toxins on one side, then have a large array of ion channels on the other side," Chait says. "Once you've married the toxins to their ion channels, you're likely to find something that is medically useful."