The most complete catalog of proteins in king cobra venom yet

Now, in a paper published in the journal Molecular & Cellular Proteomics, a team of researchers reveals a detailed account of the proteins in the venom of king cobras. "I believe this study to be one of the most complete and precise catalogues of proteins in a venom yet obtained," states Neil Kelleher at Northwestern University, one of the study's senior investigators.

Snake venoms always have intrigued scientists, because they "have a rich diversity of biological activities," says Kelleher's collaborator Gilberto Domont at Universidade Federal do Rio de Janeiro in Brazil. Among other things, venoms contain various proteases, lipases, nerve-growth factors and enzyme inhibitors. Besides understanding how venoms function, researchers want to develop better antidotes to snake venom and identify molecules from venom that can be exploited as drugs, such as painkillers, anticlotting medications and blood pressure treatments. Domont points to captopril, a drug now commonly used to treat high blood pressure and heart failure. It was derived from a molecule found in the venom of a poisonous Brazilian viper.

Although the venom of the king cobra, the largest venomous snake in the world, which can stretch up to 13 feet, has been analyzed previously, questions persist about the venom. How do the sequences of the toxins evolutionarily vary? How do some post-translational modifications on proteins make the venom lethal? But to answer these questions, researchers need a proper count of the proteins in king cobra venom.

The advent of proteomics has allowed scientists to survey the rich diversity of proteins in a given sample. There are different approaches that rely on mass spectrometry to carry out proteomic analyses. One approach is called top-down proteomics. It allows researchers to look at proteins as whole, intact entities. In the more conventional approach, called bottom-up proteomics, proteins are cut into bite-sized fragments for analysis.

In bottom-up proteomics, researchers have to use computer algorithms to stitch back together protein fragments identified by mass spectrometry. Top-down proteomics avoids this problem. Its biggest advantage is that it can capture variations within the proteins as well as post-translational modifications.

Kelleher's group is one of the leaders in developing top-down proteomics, so that's what the investigators decided to use to analyze king cobra venom. Domont, Kelleher, Domont's graduate student, Rafael Melani, and colleagues obtained venom from two Malaysian king cobras held at the Kentucky Reptile Zoo. They analyzed the venom by top-down proteomics in two modes, denatured and native. In the denatured mode, the protein complexes were taken apart; in the native mode, the venom was kept as is so the protein complexes remained intact.

The investigators identified 113 proteins in king cobra venom as well as their post-translational modifications. Only 17 proteins had been known in king cobra venom