Virus particles in crystal sarchophagus

Insect viruses are indestructible thanks to their crystal structure - why is this important? Find out here.
18 March 2007

Interview with 

Peter Metcalf University of Auckland


Chris - Peter Metcalf from the University of Auckland, New Zealand has uncovered a very interesting crystal structure of an insect virus. It makes these things in cells and they behave a bit like a viral sarcophagus, the virus gets locked away inside this crystal structure and it protects the virus when it gets out of the insect and into the soil. These things wait for hapless insects to come by and then infect them. He's published this in the journal Nature recently so its obviously an important discovery, its been a mystery for sometime though hasn't it peter, how these things worked?


Peter - Yes these crystals have been known since the end of the 19th Century and they were the first and only viruses that you can see with a microscope. People have always been puzzled as to what these crystals are and it turns out that these crystals actually contain virus particles. These are much too small to be seen with a microscope.

Chris - How many are in each crystal Peter?

Peter - Each crystal contains thousands of virus particles, so the actual infectious object that the insect eats when it gets infected is a little crystal containing virus particles.

Chris - Why does it need to resort to that, because there are lots of viruses around that don't use this technique, so why do these insect viruses have to make these clever sarcophagi to lock themselves into?

Peter - Nobody really knows that but what we thing is the crystals stabilise the virus, most viruses don't last very long in the environment, but these crystals containing the viruses last for years and years. In fact when you eat a cabbage from the supermarket you're likely to be eating these viruses because the crystals last so long, they're really impossible to get rid of.

Chris - How did you break the structure of them? How did you work out what they were made of these crystals?

Peter - Whilst the crystals are big enough to be seen by a light microscope they're very small compared to the crystals that protein crystalographers generally use. So we're X-ray crystalographers and we use a very special new micro X-ray beam at the Swiss light source which is a synchrotron near Zurich. We use this beam to shoot these crystals to figure out the atomic structure.

Chris - So the X-ray goes into the crystal it gets bounced about all over the place and the pattern of beams of light that come out tell you something about how the atoms must be arranged inside the crystal.

Peter - That's right, exactly.

Chris - So now you've sussed this out does it tell you anything useful in terms of how we might be able to exploit these particular crystals for medicine or technology?

Peter - Yes, it certainly does because what we did was to figure out the atomic structure of the crystal so we know how they're made in great detail and that means that we can modify them and the interesting thing is we found inside the crystal nucleotides (the sub-units of DNA) and that means that we can put other things in these crystals and we also know how to put things into crystals instead of the virus. So the crystals can be used as micro containers, very small objects containing other things and stabilising them.

Chris - So given that you can stabilise a virus naturally, that's how the insect virus works, a big problem in the third world with vaccines is keeping things in a fridge because third world countries don't have power for long enough to power fridges. Could you therefore use this as a novel kind of vaccine technology where you could put very fragile viruses inside these things? They would be stabilised, they could then be transported all over the place and given to people when they needed them and they would protect them.

Peter - Yes, that's certainly one of our thoughts. There's a whole variety of applications , the lack of stability of proteins in general is a big problem in biotechnology and so a nice method like this for stabilising them is generally important.


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