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Updated: December 4, 2013 16:55 IST

King cobra genome sequenced

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A young king cobra as seen on a tree branch near Shimoga. Photo: Special Arrangement.
The Hindu
A young king cobra as seen on a tree branch near Shimoga. Photo: Special Arrangement.

Scientists have sequenced the entire genome of the world’s longest poisonous snake - king cobra - and uncovered the secrets behind its deadly venom.

King cobras, capable of growing up to 18.5 feet in length, can be found in forests of India and throughout southeast Asia.

Researchers from the Liverpool School of Tropical Medicine, along with a team of international biologists, also analysed the genome of the Burmese python (Python molurus bivittatus) and used it for comparison with the king cobra (Ophiophagus Hannah).

These are the first snake genomes to be sequenced and fully annotated.

The findings have revealed dynamic evolution and adaptation in the snake venom system, which seemingly occurs in response to an evolutionary arms race between venomous snakes and their prey.

Snake venoms are complex protein mixtures encoded by several gene families and these proteins function synergistically to cause rapid paralysis or death in prey.

The study provides an insight into the biology of the venom in snakes, and allows the understanding of the evolution of venom genes at the genome structural level.

Researchers found that despite previous hypotheses that venom genes evolve “early” in the lineage leading to snakes, venom gene families do not duplicate early, in fact the study shows that the rapid and extensive expansion of functionally important venom toxin families is restricted to the venomous “advanced” snake lineage.

The diversification of these toxins correlates directly with their functional importance in prey capture.

The most pathogenic king cobra toxin family have undergone massive expansion, while, in contrast, venom proteins with less important functions do not participate in the evolutionary arms race between snakes and their prey.

“These are the first snake genomes to be sequenced and fully annotated and our results in relation to the king cobra provide a unique view of the origin and evolution of snake venom, including revealing multiple genome-level adaptive responses to natural selection in this complex biological weapon system,” said co-lead author of the study Dr Nicholas Casewell at LSTM.

“These adaptations include the massive and rapid expansion of gene families that produce venom toxins, providing the snake with a highly toxic protein mixture required to overcome a variety of different prey and also circumvent any resistance to venom that may have developed in such prey.

“Our study provides unique genome-wide perspectives on the adaptive evolution of venom systems as well as protein evolution in general.

“As such it contributes an essential foundation for understanding and comparing evolutionary genomic processes in venomous organisms,” Mr. Casewell said in the study published in the Proceedings of the National Academy of Sciences (PNAS).

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