Thursday, 2 February 2012

A shark defeated 50 viruses today, what did you do?

Great white & lunch
As if sharks weren’t cool enough- dominating the underworld and terrifying mainland inhabitants that brave the waters of their territory, but it is now known that sharks are even capable of conquering the smallest pests not even our most advanced technology can beat.  A recent paper published in the Proceedings of the National Academy of Sciences describes the unexpected broad-spectrum antiviral properties of a protein found in the tissues of dogfish sharks and white blood cells (immune system cells) from sea lampreys. 

The most interesting facet of this discovery is the mechanism by which the protein acts to ward off pathogens like viruses from entering and infecting the host’s cells. Squalamine, the protein of interest here, has a chemical composition that allows it to neutralize the charge on the inner side of the barrier that protects cells. Why is neutralizing the inner barrier of cells the magical antiviral mechanism? Imagine viruses as mini Rubik’s cubes, but with 60 subunits forming the outer shell structure of a 20-sided sphere instead of a cube. If you have never seen a Rubik’s cube I suggest you exercise your right to free images and information from Wikipedia and pick yourself up out of grade 1. So this 20-sided sphere-like structure that viruses possess serves as a shell to protect the genetic material and guts of the virus that allow it to reproduce and multiply in their infected hosts. Amazingly, the outer shell can also feature proteins that stick out and serve as antennas. These antennas seek out reciprocal signals from cells they want to infect. In the scenario of Squalamine, shark cells, and a virus- imagine the virus with its antenna protein trying to bind to a reciprocal protein on a shark cell to transmit a signal and being unable to transmit this signal and enter the cell to infect the cell because a defending protein (Squalamine) is hanging out against the inner side of the barrier blocking the virus-shark cell signal. The virus’ antenna-like protein typically searches for a negatively charged signal in a host cell barrier, but Squalamine carries a positive charge and as it interacts with a cell barrier (also known as the membrane) it neutralizes the electrostatic charge of the barrier. A neutral barrier is not a happy barrier if you’re a virus trying to get across! 

So there you have it, in a nutshell, Squalamine: a positively charged super protein from sharks, exerts its super powers, shutting down the border for viruses like Dengue virus, Hepatitis B virus, Yellow Fever virus, and Herpesviruses that infect humans and Eastern Equine Encephalitis Virus that mostly causes fatality in horses. Next time you see the ads for Shark Week on Discovery, I hope you will not only find excitement in watching Great Whites catch air and mangle seals from the waters, but you will appreciate their true greatness in harboring a potential magic bullet therapy against some of the wickedest viruses plaguing our world today.  

For reference, the PNAS paper can be found here:

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