Venomous bite: Harmless digestive enzyme evolved into venom in two species

Oct 29, 2009
A harmless digestive enzyme can be turned into a toxin in two unrelated species — a shrew (pictured) and a lizard — thereby giving each a venomous bite. Courtesy of the University of Michigan Museum of Zoology

(PhysOrg.com) -- Biologists have shown that independent but similar molecular changes turned a harmless digestive enzyme into a toxin in two unrelated species -- a shrew and a lizard -- giving each a venomous bite.

The work, described this week in the journal by researchers at Harvard University, suggests that protein adaptation may be a highly predictable process, one that could eventually help discover other toxins across a wide array of species.

"Similar changes have occurred independently in a shrew and a lizard, causing both to be toxic," says senior author Hopi E. Hoekstra, John L. Loeb Associate Professor of the Natural Sciences in Harvard's Department of Organismic and . "It's remarkable that the same types of changes have independently promoted the same toxic end product."

Lead author Yael T. Aminetzach, a postdoctoral researcher in the same department, suggests that the work has important implications for our understanding of how novel protein function evolves by studying the relationship between an ancestral and harmless protein and its new toxic activity.

"The venom is essentially an overactivation of the original digestive enzyme, amplifying its effects," she says. "What had been a mild in the salivary glands of both species has become a much more extreme compound that causes paralysis and death in prey that is bitten."

In the first part of the study, Aminetzach and her colleagues compared a toxin found in the salivary glands of the insectivorous North American shrew Blarina brevicauda to its closely related digestive enzyme kallikrein. Enzymes are proteins that catalyze, or increase the rates of, chemical reactions; this rate enhancement occurs at a specific region on an enzyme called the active site.

Aminetzach found that the specific molecular differences between kallikrein and its toxic descendent are highly localized around the enzyme's active site.

" is fostered by three specific changes that increase enzyme activity," Aminetzach says. "The active site is physically opened up, and the loops surrounding it become more flexible. The area around the active site also becomes positively charged, serving to better guide the substrate directly into the active site."

To further demonstrate that these molecular changes to kallikrein are related to the evolution of toxicity, Aminetzach explored the evolution of another kallikrein-like toxin in the Mexican beaded lizard (Helodermata horridum). She found that this toxin, while distinct from the analogous toxin in the shrew, nonetheless exhibits the same catalytic enhancement relative to the original kallikrein enzyme.

Equally important, she found that this functional change in the lizard toxin is accomplished through similar molecular modifications of kallikrein, and through identical mechanisms of structural alteration of the active site, as in the shrew toxin.

This insight -- namely, that toxins could arise by increasing the catalytic activity of enzymes through a conserved and predictable mechanism -- could be used both to identify other kallikrein-derived toxic proteins and as a method to evolve new function in general.

Source: Harvard University (news : web)

Explore further: Study finds fish just wanna have fun

add to favorites email to friend print save as pdf

Related Stories

Evolution mystery: Spider venom and bacteria share same toxin

Feb 01, 2006

It's a case of evolutionary detective work. Biology researchers at Lewis & Clark College and the University of Arizona have found evidence for an ancient transfer of a toxin between ancestors of two very dissimilar organisms--spiders ...

Snake venoms share similar ingredients

Dec 20, 2007

Venoms from different snake families may have many deadly ingredients in common, more than was previously thought. A study published in the online open access journal BMC Molecular Biology has unexpectedly discovered three- ...

Unlocking the function of enzymes

Nov 06, 2007

Fitting a key into a lock may seem like a simple task, but researchers at Texas A&M University are using a method that involves testing thousands of keys to unlock the functions of enzymes, and their findings could open the ...

A Change for the better: Improving properties of enzymes

Sep 24, 2009

An international team of scientists from the Czech Republic, Germany and Japan have developed a new method for improving the properties of enzymes. The method has potential for wide application in the chemical, ...

Scientists Use Light to Control Proteins

Oct 16, 2008

A team of researchers from Penn State and the University of Texas Southwestern Medical Center has discovered a way to use light to control certain proteins that catalyze biochemical reactions. "This is one ...

Recommended for you

'Red effect' sparks interest in female monkeys

Oct 17, 2014

Recent studies showed that the color red tends increase our attraction toward others, feelings of jealousy, and even reaction times. Now, new research shows that female monkeys also respond to the color red, ...

User comments : 0