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Scorpion toxin tells an evolutionary tale.



Scorpion toxin tells an evolutionary tale

To thrill visitors at his lab, Herve Rochat sometimes picks up a scorpion and rubs its belly with his finger. Do not try this at home.

The venom that trickles from the tail of the tickled arachnid arachnid (ərăk`nĭd), mainly terrestrial arthropod of the class Arachnida, including the spider, scorpion, mite and tick, harvestman (daddy longlegs), and a few minor groups.  contains a cocktail of powerful, protein-based toxins that has kept Rochat and his co-workers busy for two decades. In the Jan. 22 BIOCHEMISTRY, the team reports the discovery of a scorpion toxin that may represent a molecular ancestor of the dozens already identified by scientists who study scorpion venom.

Scorpions, notorious for the defnesive stings they inflict when disturbed by humans, also use their poisons offensively to paralyze par·a·lyze
v.
To affect with paralysis; cause to be paralytic.
 prey such as insects, other scorpions or small vertebrates. Their specific neurotoxic neurotoxic

pertaining to or emanating from a neurotoxin.


neurotoxic state
a case of poisoning by a neurotoxin.


neurotoxic adjective
 action makes these chemicals useful as molecular tools for studies of nerve-cell behavior. They may also hold promise as models for safer and more selective insecticides.

Biochemist Erwann P. Loret, working with Rochat's group at the National Center for Scientific Research in Marseilles, France, isolated the new toxin from the venom of the North African North Africa

A region of northern Africa generally considered to include the modern-day countries of Morocco, Algeria, Tunisia, and Libya.



North African adj. & n.

Adj. 1.
 speices Androctonus australis Hector. In Greek, Loret notes, androctonus means "killer of man." These large scorpions--some the size of a hand--kill several thousand people each year, estimates biologist Gary A. Polis of Vanderbilt University Vanderbilt University, at Nashville, Tenn.; coeducational; chartered 1872 as Central Univ. of Methodist Episcopal Church, founded and renamed 1873, opened 1875 through a gift from Cornelius Vanderbilt. Until 1914 it operated under the auspices of the Methodist Church.  in Nashville. The molecular diversity of their venomous venomous

secreting poison; poisonous.
 brew limits the effectiveness of current antivenom antivenom Antivenin Toxicology A vehicle that contains an antibody or other substance that binds specifically to a toxin, deactivating it  treatments, notes Dean D. Watt, a scorpion venom specialist at Creighton University School of Medicine in Omaha, Neb.

Although the newly identified toxin, labeled AaH IT4, doesn't rank among the most potent scorpion poisons, it stands out in its ability to smile both mice and insects, says Loret, now at Oregon State University Oregon State University, at Corvallis; land-grant and state supported; coeducational; chartered 1858 as Corvallis College, opened 1865. In 1868 it was designated Oregon's land-grant agricultural college and was taken over completely by the state in 1885.  in Corvallis. Laboratory experiments show that AaH IT4, like anti-insect toxins secreted by other "Old World" scorpions, paralyzes insect larvae Larvae, in Roman religion
Larvae: see lemures.
 by binding to sodium channels on the larvae's nerve-cell membranes. And, like anti-mammal toxins from "New World" scorpions in North and South America, it also kills mice. Although researchers have identified several New World scorpion toxins that show both anti-insect and anti-mammal action, those toxins bind to only one of two possible sites on mammalian sodium channels. AaH IT4, unlike any other scorpion toxin known, can bind to either type of site on mammalian cells while also possessing anti-insect properties.

This unprecedented breadth of action suggests that AaH IT4 is an "ancestral scorpion toxin," Loret and his co-workers assert. According to their reasonin, it's a more primitive, less specialized toxin that covers more ground at the expense of potency.

That flexibility shows up in the toxin's molecular structure: a folded string of 65 amino acids that does not include the amino acid proline proline (prō`lēn), organic compound, one of the 20 amino acids commonly found in animal proteins. Only the l-stereoisomer appears in mammalian protein. . Loret believes the absence of proline allows the molecule to change its shape so that it can conform to any of several sodium-channel sites featuring subtly different configurations. A strict molecular shape would restrict the toxin's versatility.

Loret plans to use AaH IT4 to study why some scorpion toxins affect only insects while others affect only mammals and other vertebrates. In the long run, he and others hope to exploit this natural selectivity to design potent new insecticides. Watt, noting that scorpion toxins appear effective only when injected, suggests that getting scorpion-inspired insecticides into their targets will take some technical creativity.

Most early investigations of scorpion venom focused on the development of antidotes or vaccines, but the various toxins have now become an important research topic in their own right. "In science," says Loret with a laugh, "you begin working on a serum antidote and you may end up with an insecticide."
COPYRIGHT 1991 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:venom's molecular ancestor
Author:Amato, Ivan
Publication:Science News
Date:Feb 9, 1991
Words:595
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