ASU Research E-Magazine: Toxins as Tools

Allan Bieber uses the toxins from rattlesnake venom to study the human body. That’s correct—he uses snake venom as a tool. By looking at how venom messes up the body’s normal functions, Bieber gets a better understanding of how those functions occur.

Bieber is an ASU professor of chemistry. He says that snake venom is a good tool because it targets very specific parts of the body. For example, one type of venom stops brain cells from communicating. Another type disintegrates muscle tissue.

Most toxins in snake venom are proteins. Proteins play vital roles in the operation of the human body. Some proteins form structures like hair and muscle. Other proteins have distinct jobs. They make up antibodies that protect us against infectious disease, hormones that send instructions to body parts, and enzymes that promote chemical reactions.

“Proteins carry out a lot of important functions in cells,” Bieber says. “Virtually every chemical reaction in the cell occurs in the presence of a catalyst. Most catalysts are proteins. It’s important to understand the structure of these proteins in order to get some handle on what they do and how they do it.”

The proteins in snake venom carry out functions in the human body, just like our own proteins. For example, many types of venom contain enzymes that trigger chemical reactions. Natural enzymes work to help the body, but the enzymes in snake venom have harmful effects.

Bieber studies the venom of the Mojave Rattlesnake, which is found extensively throughout Arizona. The Mojave’s venom contains a poison called a neurotoxin. Neurotoxins affect nerve cells, or neurons, and can cause paralysis and eventually, death.

Neurotoxins work by preventing neurons from communicating with each other. Normally, neurons communicate using chemical messengers called neurotransmitters. Neurotransmitters regulate all kinds of bodily activities and states, from physical activities like movement, to sensations like hunger, or emotions like anger. Neurotransmitters travel between neurons through a fluid-filled space called the synapse.

Rattlesnakes can produce two types of neurotoxins. The first type targets neurons that send the messages and prevents them from releasing neurotransmitters. These pre-synaptic neurotoxins work before the neurotransmitters enter the synapse.

The second type targets the neuron that is designed to receive the message by blocking the receptors that take in neurotransmitters. This type is called a post-synaptic neurotoxin. It does its work after the neurotransmitters enter the synapse.

Think of neurotransmitters as being like letters mailed through the post office. If you were trying to send a letter to a friend, a pre-synaptic neurotoxin would stop you from mailing the letter. A post-synaptic neurotoxin would jam up your friend’s mailbox so that the mail could not go in. Either way, your friend would not get the letter.

“[Both toxins] have the same overall effect—respiratory paralysis. But the sequence of events is different,” Bieber says.

Neurotoxins are just one kind of poison found in snake venom. Different snakes carry different kinds of toxins. Some venoms, called myotoxins, damage muscle cells. Others interfere with the blood clotting process. Still others actually promote clotting.

In addition, a single venom can have different effects on different types of cells. Bieber has experimented with using neurotoxins on muscle cells. He found that venom toxins dissolve fully formed muscles, but have no effect on myoblasts, the “baby” cells from which muscles grow. These results gave him some clues about the structure of the different cells.

“The results tell us that there is something different about the cell surfaces,” he says.

Because venoms have such destructive effects, Bieber does not conduct experiments on people or animals. Instead, he uses cell cultures that are grown in a laboratory.

“Cell cultures allow us to use the same cell line throughout,” he says. “The other advantage is that we can do a lot of experiments, because there are lots of cells.”—Diane Boudreau