Protein crystallisation under microgravity conditions: What did we learn on TIM crystallisation from the Soyuz missions ?

The protein Triose Phosphate Isomerase from the hyperthermophilic organism Thermotoga maritima was crystallised on board of the International Space Station in the framework of the Soyuz missions. In this paper we report on the following observations. Firstly different crystallisation techniques and environments can result in different crystal forms for the same crystallisation conditions, presumably due to the change in rate at which supersaturation is achieved. Secondly, the X-ray quality of the crystals grown in the ISS is largely superior to their ground control crystals. Mimicking microgravity on ground, by adding a small amount of gel to avoid convection, results in a substantial improvement of X-ray quality. Nevertheless in our analysis the crystals obtained in this gelled ground environment are of a slightly inferior quality as compared to their space homologues. Finally crystals, grown in the International Space Station are moving in the capillaries, not only because of g-jitters but also due to residual accelerations, severely modifying the solubility and concentration gradients.