Cobras deal with their venom differently from vipers, the scientists suspected. During the 1990s studies were launched to find out why.
Snake venoms are complex mixtures of peptides, enzymes, and other toxins that target the nerves, muscles, and blood circulation and coagulation. A key to the research was finding how the toxins reacted with muscle receptors.
Lock and Key
Takacs cloned a cobra's acetylcholine receptor and compared it to acetylcholine receptors from other vertebrates (animals with spinal columns). At the molecular level this cobra receptor looked the same as those in the rest of the vertebrates—except for a single different amino acid.
Takacs' experiments showed that this single difference introduces a bulky sugar molecule onto the cobra receptor. The sugar masks the so-called binding site on the receptor surface—which prevents the neurotoxin from attaching.
"If the sugar is removed, then the cobra receptor will become sensitive to its own neurotoxin, just as other animals are," Takacs explained.
To prove his theory, Takacs and his colleagues engineered a mouse muscle receptor with a sugar molecule attached—and thus created a mouse receptor that resists cobra neurotoxin.
"Like a keyhole and a key—if you change the keyhole, the key will no longer fit into it," Takacs said. That's the secret to how the cobra avoids its own venom.
"These same venom [and receptor] molecules, once purified, characterized, redesigned, and cloned, can be used in medical research as possible drugs for treating strokes, heart attacks, and metastasis as well," said John C. Perez, a professor at the Natural Toxins Research Center at Texas A&M University-Kingsville.
"These venom and receptor molecules all have important biomedical applications, making Takacs's work much more than just studying snake venom," he added.
For more on cobras, watch National Geographic Presents: King Cobra Sunday, February 22, at 9 p.m. ET/PT in the United States—only on the National Geographic Channel.
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