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Common origin for snake venom and mammalian salivary protein

Some snakes, some lizards, and some mammals bite and produce venom. The strains of these species differentiated over 300 million years ago, but the venom they carry evolved from salivary proteins of the same ancestry, according to BMC Biology.

Research teams at the Okinawa Graduate University of Science and Technology (OIST) and the Australian National University have traced their origins by focusing on a group of toxins called “kallikrein serine proteases” found in most snake venoms, reptiles, and all mammalian venoms. , Found a gene found in a common ancestor.

Agnes Balua, an OIST PhD student and one of the co-lead authors of this research paper, explains: “Venom is a cocktail of toxic proteins that has evolved throughout the animal kingdom as a way to kill prey and block movement. The system of venom from the mouth found in snakes is particularly complex, and the origin of the venom is It’s not clear yet. ”

In a previous paper, Barua’s research team found that mammalian salivary glands and snake venom glands have similar activity patterns for a group of regulatory genes, and the basis for venom evolution is snakes and mammals. It suggests that it exists in both.

“In my last paper, I hypothesized that snakes and mammalian ancestors shared a common set of genes with the ability to carry toxins. After that, snakes and mammals evolved differently. In the snake lineage, the toxin mixture has diversified and become more toxic, and the venom has evolved in mammals, but only to a very low degree, but what we wanted to know was that of mammals and snakes. Was the toxin contained in the venom evolved from a common ancestral gene? ”

Kallikrein serine proteases are a type of proteolytic enzyme and play an important role in regulating blood pressure. Mammalian saliva contains small amounts of these proteins, but their function remains unknown to this day. However, in venomous snakes and mammals such as shrews and solenodon, the toxicity of these proteins is evolving, and high doses can cause a rapid drop in blood pressure that can lead to loss of consciousness and even death. ..

Researchers have long been aware that kallikrein serine proteases are biochemically similar to those found in snake venom and mammalian saliva, but are they actually related? Has never been revealed. “There are so many similar serine proteases that it has been difficult to isolate the genes needed to elucidate the evolutionary process,” says Barua.

The research team was able to identify and compare all kallikrein genes in reptiles, amphibians, fish and mammals and create an evolutionary tree using recent advances in genomic analysis.

Surprisingly, we discovered that the snake venom kallikrein serine protease and kallikrein in mammalian saliva evolved from the same ancestral gene.

Barua explains: “This is really strong evidence to support our hypothesis that venom evolved from a common set of genes of ancestral toxic abilities, but most surprisingly found in humans and mice. Non-toxic salivary calicrane, such as, also evolved from genes of the same ancestry. ”

In fact, the researchers found that the non-toxic kallikrein in mammalian saliva is closer to the snake venom toxin than other mammalian kallikreins.

From the above, it is considered that a protein called salivary kallikrein in mammals including humans also has the ability to evolve to be toxic.

However, Mr. Barua immediately added the following note. “Just because we have the elements to evolve to have venom doesn’t mean that it actually happens. It’s so expensive to make venom, so it evolved that way. There is strong ecological pressure

So what this reveals is that “the boundary between mammals with and without venom has become more ambiguous than previously thought,” Barua concludes.

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