For the first time, researchers were able to determine the structure of a protein while still inside a living cell with an X-ray laser
These successes have opened new avenues that led to many discoveries, such as the structures of enzymes and DNA. It is not surprising that the United Nations has declared 2014 International Year of Crystallography.
The X-ray diffraction is limited to the crystals
Physicists, biologists and chemists, among which may be mentioned John Bernal, Linus Pauling, Max Perutz, Dorothy Hodgkin and Aaron Klug, will be interested in the 1930s to determine the structure of certain organic molecules, including proteins and vitamins, using the techniques of X-ray diffraction This work will culminate in 1953 with the discovery of the structure of hemoglobin, for which Max Perutz and John Kendrew will drop out the Nobel prize in Chemistry in 1962, and that of DNA by Watson and Crick, through a diffraction pattern obtained by the British biologist Rosalind Franklin.
Nowadays, the determination of the structure of biological molecules by X-ray diffraction is still a very active field, since it allows the development of all kinds of drugs. One strategy used to understand particular protein structure is to study crystalline form. But this study takes place in vitro, we can not be sure of the actual structure of these proteins when they are still within living cells, ready to participate in biochemical reactions.
To eliminate this bias, researchers have sought to develop a technique of X-ray diffraction that would make measurements in vivo. To this end, they have turned to the X-ray lasers in development for a number of years. An article published in PNAS reported a first success in this direction with the Linac Coherent Laser Light Source of the famous SLAC in California.
An X-ray spied protein in bacteria
The international team of researchers used the LCLS laser was interested in a well-known name of Bacillus thuringiensis (Bt) bacterium, living everywhere in soil and water. It is unusual to synthesize and excrete protein in crystal form that is toxic to insects. Protein crystals are present in the bacteria itself. Experiments were therefore conducted to determine the structure of the crystals inside the cells. To this, a solution containing Bt bacteria was subjected to laser pulses, and over 30,000 figures X-ray diffraction were obtained. They were processed by computer with the mathematical tools of the Fourier analysis, which allowed to reconstruct the 3D structure of proteins.
Successful strategy with the key to the first determination of the structure of a protein in vivo. The results of the experiment showed that at least in this case, there was no difference between the structure of the in vivo and in vitro protein. So it seems that one is indeed able to build a new tool to understand what is going on inside living cells.
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