ISS Research Results: Protein Crystal Growth (PCG) Single-locker Thermal Enclosure System (STES)

Results

The crew deactivated the final PCG-STES experiment cylinders on April
9, 2002. Both units have been transferred to the Shuttle Atlantis, which
docked with the Station on April 10, for return to Earth. Two more PCG-STES
units are scheduled to be delivered to the Station for mission UF2 later
this year.

After
an accidental computer shutdown
on Monday, February 4, interrupted Station attitude control, which allows
the solar arrays that produce the Station’s power to remain angled toward
the sun, all payloads and several onboard systems were powered down as
a power-saving measure. Within 6 hours, power was returned to EXPRESS
Rack 4, which houses the most power-sensitive payloads, like PCG-STES.
Fortunately, the temperature inside the STES unit rose slowly during the
power-down, so the science team are hopeful that the stress to the samples
stored inside was minimal. All nominal Station operations were restored
within 24 hours. The science team plan to activate a cylinder in the second
PCG-STES unit on Station on Friday, February 8. The Increment 4 experiments
were first activated on December 6.

The
first STES units on Station were activated in May 2001. All the experiments
were completed by mid-July. Both units operated as expected and were returned
on STS-104. This flight produced an unusually low yield: only 23.8 percent
of the chambers produced crystals. The principal investigator attributed
the low yield to the delayed start (16 days after being loaded in their
chambers) of the experiment. Ground-based control experiments conducted
prior to the STS-100 launch resulted in similar yield. Based on this information,
the Increment 4 PCG-STES experiments were activated sooner.

Previous
Shuttle flights of STES with the PCAM have consistently yielded larger
crystals with at least a 10 percent increase in diffraction and between
0.0 and 0.3 Å improvement in resolution (i.e., better-ordered, higher-quality)
over crystals grown from the same solution on Earth. On STS-85, a 1.7
Å structure of HIV protease-inhibitor complex using the PCAM. Previous
crystals grown of this inhibitor were too small for diffraction analysis.

Applications

Structural
studies of microgravity-grown protein crystals may provide information
for the development of new drugs.  For example, X-ray diffraction
studies have led to more effective treatments for diabetes.  Previous
PCG-STES experiments focused on health include virus structure and therapeutic
development, the biochemistry of sickle-cell anemia, liver cell regeneration,
and vaccine development and drug delivery.

In
addition, PCG-STES provides a  variety of options for hardware configuration
in a temperature-controlled environment.  The PCAM allows high-quality
crystals to not only be grown and stored until they are returned to Earth,
but also allows postflight shipping without disturbing the crystals, making
it a desirable platform for commercial and noncommercial protein crystal
growth experiments.

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