Microgravity protein crystallization: are we reaping the full benefit of outer space?

Protein crystallography, which has a growing role in the human genome project, is one of the most powerful techniques in modern biology. However, it can only be applied providing suitable crystals can be obtained. The ability to produce suitable crystals is currently the major bottleneck to structure determination. Microgravity, which is used as a tool for improving crystal growth, is a high-profile enterprise, especially with the upcoming prospects for utilizing the International Space Station, yet the issue of crystallization in microgravity is an extremely controversial one. In spite of numerous experiments conducted in microgravity during 16 years, the reported success rate, measured in terms of various improvements witnessed in the perfection of protein crystals, has been a mere 20%. In this paper we present experimental evidence, supporting previous fluid physics calculations to show that in many cases the potential benefits of the microgravity environment have not been fully exploited. These findings offer an explanation for the low rate of success and open up the possibility for enhancing the efficiency of experimentation in microgravity. Furthermore, these findings extend into a number of other disciplines involving fluid physics.