Protein crystal growth in space, past and future

Abstract

The Center for Biophysical Sciences and Engineering (CBSE) at the University of Alabama at Birmingham has performed protein crystal growth experiments on more than 39 US space shuttle missions. Results from these experiments have clearly demonstrated that the microgravity environment is beneficial in that a number of proteins crystallized were larger and of higher quality than their Earth-grown counterparts. Improvement in crystal quality is judged by analysis of ultimate diffraction resolution, individual peak mosaicity, and electron density maps. There are now a number of protein crystals that exhibited resolution improvements of 0.5–1.5 Å. Mosaicity studies revealed dramatic decreases in peak widths for the microgravity-grown crystals. These microgravity results plus data from a variety of other investigators have stimulated various space agencies to support fundamental studies in macromolecular crystal growth processes. The CBSE has devoted substantial effort toward the development of dynamically controlled crystal growth systems which allow scientists to optimize crystallization parameters on Earth or in space. These systems enable monitoring and control of the approach to nucleation and post-nucleation growth phases, thereby dramatically improving the crystal size and X-ray diffraction characteristics. The CBSE is currently designing a complete crystallographic laboratory for the International Space Station including: a crystal growth rack, which will support a variety of crystallization hardware systems; an X-ray diffraction rack for crystal characterization or a complete X-ray data set collection; and robotically controlled crystal harvesting/cryopreservation systems that can be operated with minimal crew time via telerobotic and/or robotic procedures. Key elements of the X-ray system include unique X-ray focusing technology combined with a lightweight, low-power source. The X-ray detection system is based on commercial CCD-based technology. This paper will describe the X-ray facility envisioned for the International Space Station.