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TMV: turning the disc into a helix


Producing a phase diagram for the A protein
Aaron Klug Scientist
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So what we did was to make large quantities of protein, change the salt conditions, change the temperature and look at the aggregates, either by hydrodynamics using ultra centrifuge or by... and by electron microscopy and so on. And so we produced a phase diagram, the first time anybody had ever done it for a protein, but a very common physical chemistry of small... small molecules. We plotted the different states of aggregation of the TMV protein as a function of pH as a function of temperature. And lo and behold it told us something that had already been observed, been observed by others, that if you put the TMV protein, the so called A protein, the... the proposed or supposed trimer at low pH, low acid conditions, it formed... it formed a helix without any RNA. So the protein determined the protein... a helical array of proteins was determined purely by the properties of the protein; this was only a low pH. However, if you went to high alkali, then, of course, the thing disintegrated and... sorry, made only small aggregates of about roughly the range of a trimer. But in-between these two positions, at about a normal temperature, 20º and about a pH of 7, which is normal, what we saw were ringed shaped objects and they were the discs. The very discs that Reuben had crystallised, now this seemed to... And also, the salt condition was about .15 molar which is normal physiological condition. So I realised then that the disc was an object not adventitious, it was actually... the protein on its own at normal conditions made the disc and didn't make the virus helix. And I realised that it would be... that... it would be... I think these are Don Caspar's words, soon afterwards, it would be... but I realised... they were... it would be a disaster if the protein on its own formed the helix without the RNA. Because what he wanted to do was combine with the RNA and put the RNA into the helical array... and being biological, so it could. So that... so therefore... but the disc which is not... which is a number of rings in the disc was 17, the number of turns in the virus helix at 16 and one third, so it wouldn't require much of a change to start with the disc which would then dislocate and then start the growth of the virus just in the way that we built the Brussels model. And so now what I can't remember is whether I harked back consciously to the Brussels model but I... I must have realised at some point that was what I was just reliving that.

Born in Lithuania, Aaron Klug (1926-2018) was a British chemist and biophysicist. He was awarded the Nobel Prize in Chemistry in 1982 for developments in electron microscopy and his work on complexes of nucleic acids and proteins. He studied crystallography at the University of Cape Town before moving to England, completing his doctorate in 1953 at Trinity College, Cambridge. In 1981, he was awarded the Louisa Gross Horwitz Prize from Columbia University. His long and influential career led to a knighthood in 1988. He was also elected President of the Royal Society, and served there from 1995-2000.

Listeners: Ken Holmes John Finch

Kenneth Holmes was born in London in 1934 and attended schools in Chiswick. He obtained his BA at St Johns College, Cambridge. He obtained his PhD at Birkbeck College, London working on the structure of tobacco mosaic virus with Rosalind Franklin and Aaron Klug. After a post-doc at Childrens' Hospital, Boston, where he started to work on muscle structure, he joined to the newly opened Laboratory of Molecular Biology in Cambridge where he stayed for six years. He worked with Aaron Klug on virus structure and with Hugh Huxley on muscle. He then moved to Heidelberg to open the Department of Biophysics at the Max Planck Institute for Medical Research where he remained as director until his retirement. During this time he completed the structure of tobacco mosaic virus and solved the structures of a number of protein molecules including the structure of the muscle protein actin and the actin filament. Recently he has worked on the molecular mechanism of muscle contraction. He also initiated the use of synchrotron radiation as a source for X-ray diffraction and founded the EMBL outstation at DESY Hamburg. He was elected to the Royal Society in 1981 and is a member of a number of scientific academies.

John Finch is a retired member of staff of the Medical Research Council Laboratory of Molecular Biology in Cambridge, UK. He began research as a PhD student of Rosalind Franklin's at Birkbeck College, London in 1955 studying the structure of small viruses by x-ray diffraction. He came to Cambridge as part of Aaron Klug's team in 1962 and has continued with the structural study of viruses and other nucleoproteins such as chromatin, using both x-rays and electron microscopy.

Tags: Tobacco Mosaic Virus, TMV, A protein, phase diagram

Duration: 3 minutes, 6 seconds

Date story recorded: July 2005

Date story went live: 24 January 2008