The Granada Crystallisation Box Experiment
What is the Granada Crystallisation Box Experiment ?
Who is responsible for the experiment ?
Where is the experiment now ?
What is the interest of studying proteins crystals ?
Protein molecules are quite literally the substance of life. These vast arrays of atoms perform just about every important biochemical function inside living cells. They store and carry biological information, they act as catalysts in the hugely complex chemistry of life and they provide membranes and cell walls.
If scientists can map that structure, they can learn more about the intimate workings of life. They will then be able to use their knowledge to synthesise proteins in the laboratory, which can lead to dramatically effective drugs. This is no easy task.
What is needed to study protein crystals ?
To analyse the protein structure, scientists use a technique called X-ray crystallography - and for that technique to deliver the data they are after, they need to have structurally well-ordered crystals. But proteins do not crystallise easily and it is the perfect crystals that X-ray studies require that are especially hard to make.
How are protein crystals grown ?
The Counter-Diffusion Technique used in the Granada Crystallisation Box Experiment for protein crystallisation works in a completely different way. The technique relies on allowing a protein solution and a precipitating agent (a salt solution) to diffuse one into the other. When the two solutions are put in contact the system reaches a very high supersaturation. The result is a first precipitation of an amorphous or ill-crystalline phase of the protein forming near the interface between the two solutions. Its formation depletes the concentration of protein in the neighbouring zones. As the salt diffuses faster than the protein, it then further invades the protein solution and a new precipitation takes place. The iteration of this process results in precipitation zones of fewer crystals of larger size and higher quality than with the classical Hanging Drop Technique.
What has the International Space Station to do with the growth of protein crystals ?
The problem is that in capillaries with a diameter relevant to protein crysallisation experiments, it is impossible to avoid convection. The effects of convection can only be neglected for diameters less than 1 micron, which is much smaller than the useful crystal size for X-ray diffraction which is at least in the order of 200 microns.
On the other hands, gelling of the mother solution implies the addition of a foreign chemical to be polymerised in the mother solution, but the chemicals used are known to either retard or enchance the nucleation of some proteins which creates some difficulties when fundamental aspects of the crystallisation process are being investigated.
The weightlessness onboard an Earth-orbiting spacecraft like the International Space Station is a perfect means to obtain a convection-free environment and thus to overcome the limitations resulting from the use of small-sized capillaries or gelled solutions. Without the interference of the Earth's gravity, the size and the quality of the crystals may be improved. A combination of the Counter-Diffusion Technique with microgravity is therefore very promising for research on proteins.
Such a combination will enable scientists to properly exploit the microgravity environment on the International Space Station. In addition, the use of capillaries to grow crystals of biological macromolecules has several advantages:
- It permits the implementation of the Counter-Diffusion Technique because they ca be used as long protein chamber.
- It limits the motion of crystals due to residual acceleration and reduces the mechanical load on the crystals during the atmospheric re-entry flight back to Earth.
- By employing capillaries that are transparent to X-rays, diffraction data can be directly collected from the as-grown crystals, without the critical step of harvesting and sucking them into X-ray capillaries.
Why is there a need for the Granada Crystallisation Box Experiment
?Currently available facilities for protein crystal growth in space are not yet designed to implement counter-diffusion experiments (except three experiments using modified reactors from the Advanced Protein Crystallisation Facility (APCF) during the STS-95 mission).
Based on the above considerations, a protein crystallisation experiment using the Counter-Diffusion Technique, called the Granada Crystallisation Box Experiment was designed wich implements the Counter-Diffusion Technique in X-ray capillaries. The concept builds upon research in process modelling and process optimisation supported by ESA. The experiment allows to scan a large range of crystallisation conditions with the same sample in a single capillary. It has proven to perform very well on the ground using slightly gelled protein solution so as to prevent natural convection from occuring. The possibility of realising the same process in gel-free protein solutions in space is expected to yield even better results.
What are the scientific objectives of the Granada Crystallisation Box Experiment ?
It is also considered that experiments selected for flight on the ISS in 2001 during the Expedition 3 mission in the Advanced Protein Crystallisation Facility (APCF) will benefit from a comparison with experiments with the same macromolecule using the Granada Crystallisation Box.
How is the mission with the Granada Crystallisation Box Experiment executed ?
Launch of Progress from Baikonur took place on 21 August 2001 and it arrived at the station on 23 August 2001. After its transfer to the ISS, the Granada Crystallisation Box Experiment has been stored in a quiet located where it will stay until October 2001. It does not need any power supply and will not be handled by the ISS crew anymore until the end of the mission.
The return of the experiment to Earth is presently planned on 31 October 2001 aboard the Russian Soyuz spacecraft that will also carry the French ESA astronaut Claudie Haigneré back to Earth after the completion of the CNES/Russian Andromède mission.
How do the scientists receive and analyse the data from the experiments ?
The quality of the crystals grown in space will then be measured by X-ray diffraction by the owner of each macromolecule.
An assessment of the correlation between the crystal quality, its location in the capillary and the local convection conditions prevailing during growth will be performed for all crystals grown with the use of a numerical model developed by the MARD Centre in Naples (Italy).
What about the protection of intellectual property ?