Washington

Crystal gazers: predictions about the usefulness of space crystals have not proved true.

Space experiments in protein crystal growth have yielded no important results to date, says a report released last week by the US National Research Council (NRC).

But the space station's research facilities could be used to assess whether or not crystal growth in zero gravity could ever be worthwhile, says the report.

“At this time, one cannot point to a single case where a space-based crystallization effort was the crucial step in achieving a landmark scientific result,” concluded a study panel chaired by Paul Sigler, who before his death in January was a professor of molecular biophysics and biochemistry at Yale University. “In many of the cases that have so far been listed as successful, the improvements obtained have been incremental rather than fundamental.”

The report is just the latest criticism of the US space agency NASA's microgravity research programme, which has long touted protein crystal growth as a high-payoff area of research on board the space shuttle and eventually the space station. While the NRC was not so harsh in its judgement as a panel of the American Society for Cell Biology, which two years ago called for scrapping protein crystal growth experiments in space (see Nature 394, 213; 1998), it left little doubt that past NASA claims of important research breakthroughs have been overhyped.

“To date, the impact of microgravity crystallization on structural biology as a whole has been extremely limited,” says the NRC report. Sigler's committee found a number of reasons for this. Space-shuttle experiments have been brief and have suffered from the lack of a vibration-free environment. Only a small and insular group has been involved in the research so far. Although many private companies have signed on as partners for space experiments (which NASA press releases often emphasize), “not one has yet committed substantial financial resources”.

Another problem is determining exactly what role microgravity has played in past successes. For example, when crystals of the restriction endonuclease EcoRI complexed with DNA (EcoRI–DNA) were grown in orbit, the resulting diffraction data were significantly better than those in similar samples grown on Earth. However, says the NRC panel, it was difficult to attribute the success to microgravity alone when advanced cryogenic techniques and synchrotron radiation analysis were also used.

In fact, the higher data resolutions that are now being achieved using synchrotron sources on the ground have wiped out one of the main advantages offered by space-grown samples — crystal size.

“Although the misconception that size is crucial may persist at NASA, scientists today are interested in crystallization methods that provide higher quality crystals,” wrote the panel. And until the value of space-based crystals is proven in the case of specific research problems, the high cost of such research in orbit “is bound to engender resentment in the scientific community”.

The NRC panel makes several recommendations. First, the space agency should take action to involve more people in space-based experiments, as the current recruitment process fails to attract the best scientists and bioengineers. NASA might consider joint solicitations with the National Institutes of Health and the National Science Foundation.

The panel also advises NASA to instigate a high-profile grant programme to settle once and for all the usefulness of space-grown protein crystals. The space station, with its superior facilities and longer experiment runs, will be a suitable place to conduct such tests, it says.

“If none of the projects produces a space-grown crystal that enables a breakthrough for the structure determination of a biologically important macromolecular assembly, then NASA should be prepared to terminate its protein crystal growth program,” the report concludes.