New peptides found in platypus venom

September 13, 2012 § Leave a comment

How many of you knew the platypuses produced venom? I didn’t, until I stumbled across a Molecular & Cellular Proteomics paper that describes the peptides found in venom of this unique mammal.

The platypus is one strange critter. It’s one of two mammals to lay eggs. The other is the echidna, a close relative of the platypus. The platypus uses its bill to sense electric fields. It has webbed duck feet but is furry like a mole. (The animal almost got hunted to extinction for its fur.)

The platypus “has a combination of reptilian and mammalian features,” says Emily Wong at the University of Queensland in Australia. She adds the animal has an important evolutionary position in the phylogenetic tree, between the divergence of other mammals and birds. “Studying the platypus can tell us a lot about how mammals have evolved,” she says.

Venom spur on a platypus male. Image from http://en.wikipedia.org/wiki/File:Platypus_spur.JPG

Male platypuses have a pair of spurs on their hind limbs. These spurs spit out venom. The animals produce the venom during mating season to fight off rivals. The venom causes severe pain and can kill hunting dogs, but no human fatalities have been recorded yet.

Knowing what is in venom and its composition helps researchers understand the fundamentals of an animal’s biology. But venom also has been a rich source of drugs. As Wong points out, key drugs for the treatment of hypertension, chronic pain and type 2 diabetes have been developed from venom of the pit viper, cone snail and Gila monster, respectively.

Earlier studies have shown that the platypus venom has 19 fractions, and researchers already know that there is hyaluronidase, C-type natriuretic peptides, nerve growth factor, L-to-D-amino-acid-residue isomerase and defensin-like peptides. These polypeptides and enzymes are thought to work in concert to cause swelling, lower blood pressure and create pain. But only two of these components, natriuretic peptides and defensin-like peptides, had been fully sequenced, says Wong.

To better understand the components of platypus venom, Wong, along with Katherine Belov at the University of Sydney, led a team to characterize more platypus toxins. The investigators combined a proteomics approach with a transcriptomic approach to do so. The strategies were complementary. “The proteome tells us what is in the venom and the transcriptome tells us what is in the venom gland,” says Wong. The approach allowed the investigators to identify novel toxins without any preconceived biases.

Wong says they also took advantage of the fact that platypus venom production is seasonal. They were able to compare the cDNA expression profiles of in-season and an out-of-season venom glands to get some understanding of this uncommon mammalian venom.

Not surprisingly, Wong, Belov and colleagues found that platypus venom is different from venom from snakes and other invertebrates. “We found five venom components that have not been previously characterized in any other venom to date,” says Wong.

They also discovered distinct gene-expression profiles that distinguished the active venom gland from the inactive off-season gland. “Our results suggests that venom production is not abolished out of breeding season and leads us to hypothesize upon the other activities occurring in the venom gland out of season,” says Wong.

The investigators are looking to next analyze the novel peptides they have discovered. Perhaps one or two of these peptides may lead to a drug. The investigators are also in the process of studying the venom gland of the echidna to “gain insights into venom evolution in this important lineage,” says Wong.

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