be loaded into 23 PCAM chambers. Due to flight regulations, one compound (hexadecyltimethyl
ammonium bromide) in the sample was not eligible for flight. A new formulation was created to
replace the original sample and was used to fill 45 chambers. There was a clerical error during
the transcribing of the recipe and this affected 4 sample chambers. Of the remaining chambers,
9 produced crystals. The crystals that were produced in microgravity were large needle splays
(Kundrot, Increment Two One Year Postflight Report).
PCG-STES-IMP
The PCG-STES-IMP operated on ISS during Expedition 5. The E. coli MsbA and EmrE membrane
protein samples used did not produce crystals. Previous ground tests indicated that crystal
growth was possible. Upon examining the pedestals (part of the PCAM trays where the sample
was originally loaded) it was found that the protein drops were no longer present. The drops
also contained a detergent that is used in crystallization experiments. These drops had a lower
surface tension and were more sensitive to displacement than proteins that do not contain the
detergent. An explanation for the displacement of the drops is that the trays, PCAMs, or the
entire STES unit was bumped or jolted at some point before the experiment was initiated.
The investigator has concluded that new recipes for crystallization that use detergents are
needed in order to raise the surface tension of the protein drops so they can survive the normal
movements associated with STES unit during the round trip from ground to orbit (Chang, One
Year PostflightReport, 2003).
PCG-STES-MM
Not surprisingly, given the wide array of
materials and objectives, some samples did
produce large crystals, while other samples
produced crystals no better than those
produced on Earth. Yet other samples failed
to crystallize at all.
Crystals of MnSOD, produced during
Expedition 4, exhibited an 80-fold volume
increase when compared to the crystals
produced on Earth. The crystals that were
produced in orbit ranged from small,
needle-like crystals to large 3-D crystals.
These crystals were used for Synchrotron X-ray analysis, the use of a high-energy, adjustable
particle beam used for crystal diffraction. Through this analysis it was determined that the
diffraction resolution and quality of data for the crystals produced in microgravity were
increased when compared to the diffraction resolution of the crystals grown on Earth (Vahedi-
Faridi 2003).
Crystallized structure of a nucleosome core particle that
was grown during a previous DCAM mission on Mir.
NASA Marshall Flight Space Center image.