Protein Crystallography to Enable Structure-Based Drug Design (CASIS PCG 4-1) - 11.22.16

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Science Objectives for Everyone
All molecules have a unique shape and structure, and understanding how they are physically arranged helps scientists determine not only how they work, but how other molecules interact with them. Scientists use three-dimensional crystals to study these structures in greater detail, but large molecules are difficult to crystallize on Earth, where gravity and shear forces interfere with their formation. Protein Crystallography to Enable Structure-Based Drug Design (CASIS PCG 4-1) crystallizes a specific class of proteins in microgravity, allowing chemists to study how specific modifications affect the protein’s interactions.
Science Results for Everyone
Information Pending

The following content was provided by Kristofer Gonzalez-DeWhitt, and is maintained in a database by the ISS Program Science Office.
Experiment Details


Principal Investigator(s)
Kristofer Gonzalez-DeWhitt, Eli Lilly and Company, Indianapolis , IN, United States

Information Pending

Center for the Advancement of Science in Space (CASIS), Rockledge, FL, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
National Laboratory (NL)

Research Benefits
Earth Benefits, Scientific Discovery

ISS Expedition Duration
March 2016 - September 2016

Expeditions Assigned

Previous Missions
Handheld HDPCG has flown on SpaceX-3, SpaceX-4 and SpaceX-6. This is the first flight of this investigation.

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Experiment Description

Research Overview

  • Aboard the International Space Station (ISS), the crystallization of a medically-relevant protein in complex with a small molecule ligand may allow for more uniform crystals, with a smaller solvent content, to form. These co-crystals may be of sufficient diffraction-quality to permit accurate modelling by protein crystallography.
  • Presently, co-crystals formed by ground-based techniques demonstrate sub-optimal diffraction that may be improved if crystallization proceeds in a microgravity environment.


Structure-based drug design (SBDD) is an integral component in the drug discovery and development process. Primarily, SBDD relies on the 3-dimesional, structural information provided by protein crystallography to inform the rational design of more potent, effective, and selective drugs. This reliance on protein crystallography is contingent on the ability to obtain medium- to high-resolution diffraction-quality crystals of a protein in complex with a small molecule ligand. Crystallization in microgravity may provide a means of overcoming this bottleneck, particularly for targets in which high-resolution crystal structures are necessary.
A medically-relevant protein was selected for attempting crystallization in microgravity. The protein features two ligand binding pockets – the coordination of compounds binding within these pockets gives rise to the protein’s complex, highly-ordered mechanism of action. Inhibiting an intermediate step in substrate turnover may be of therapeutic value, but presents a challenge to crystallization, and thereby, crystal structure enablement of SBDD. The protein is not known to crystallize in an apo-enzyme form, but will readily co-crystallize with at least one binding pocket occupied with compound. Co-crystals are characterized by large unit cell dimensions, large solvent channels, and a crystal lattice conducive to compound soaking.
Protein Crystallography to Enable Structure-Based Drug Design (CASIS PCG 4-1) seeks to determine if crystallization proceeding in a microgravity environment results in more uniformly-packed co-crystals with a smaller solvent content. When soaked in the presence of a second compound, these microgravity-formed crystals are expected to diffract superior to similarly treated terra-formed crystals. Where co-crystals formed in microgravity represent an improvement over co-crystals formed by ground-based methods, resulting structures are to be used to advance the medical-chemistry effort through improved/enhanced SBDD. The CASIS PCG 4 project uses few resources, and has a flexible strategy that makes it an ideal system for ISS.
The CASIS PCG 4 hardware launches at -80°C to prevent crystal formation prior to reaching microgravity. The experiment samples in the Handheld HDPCG hardware are activated by turning the sample cells 90° clockwise to equilibrate the protein insert above the precipitant reservoir. The Handheld HDPCG hardware is transferred to +4°C temperature following activation. Samples in the PCG Cards are similarly transferred to +4°C temperature, but need not be activated prior to transfer. Following an experimental duration of 21 – 30 days, the Handheld HDPCG hardware is deactivated. Deactivation is accomplished by turning the sample cells 180 degrees clockwise. This operation turns the protein insert opposite of the precipitant reservoir and stops the experiment. The Handheld HDPCG assembly and PCG Cards is returned to Earth at +4°C.

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Space Applications
To understand how proteins are built and how they work, scientists build three-dimensional crystals, which makes it possible to study the protein’s physical structure using X-rays. But large crystals are difficult to form on Earth because gravity affects their growth. This investigation crystallizes a medically relevant protein, in combination with a small molecule called a ligand, which enables scientists to see how the molecules interact. The unique microgravity environment of the International Space Station allows the crystallization process to yield high-quality co-crystals, enabling scientists to model the molecules’ structures in great detail.

Earth Applications
Structure-based drug design (SBDD) uses the physical structure of molecules to determine how they might work as a new drug. Researchers build three-dimensional crystals of proteins, and small molecules called ligands, to study them in detail. Researchers can make minor changes to the ligand, which affects the way the molecules interact with each other. By doing this before testing molecules in clinical trials, researchers can narrow down possible drug candidates, saving costs and time. This accelerates the process of drug development, benefiting patients on Earth.

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Operational Requirements and Protocols

Time between turnover of experiment and launch is 24 hours. Experiment launches frozen at -80°C.
On-orbit, experiment hardware is stowed at +4°. Sample activation must be completed within six days following launch. Sample removal and deactivation can occur within 25 days following activation. On return to Earth, temperature cannot fall below +2°C, and temperature cannot exceed 10°C.
Early recovery at the dock is required, samples are shipped to the Principal Investigator’s laboratory.

The Handheld HDPCG assembly and PCG Cards are transferred from cold stowage on the ascent vehicle to the ISS. To activate the experiment samples in the Handheld HDPCG hardware, an Activation Tool (which is attached to the side of the HDPCG hardware using Velcro) is removed and attached to each of the five cell blocks. Each cell block is turned 90° clockwise to align the sample insert with the precipitant solution. Following activation, the HDPCG assembly is transferred to refrigerated storage at +4°C. The PCG Cards need only to be transferred to refrigerated storage at +4°C to become activated. Crystals grow for 21 – 30 days. The Handheld HDPCG assembly is removed from storage for experiment deactivation. Deactivation is accomplished by attaching the Activation Tool to each cell block and turning 180° clockwise to turn the protein insert opposite of the precipitant reservoir. Prior to unberth, the HDPCG assembly and PCG Cards are transferred to refrigerated (+4°C) stowage on the descent vehicle for return.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites

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