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Comparison of the three‐dimensional structures of a human Bence‐Jones dimer crystallized on Earth and aboard US Space Shuttle Mission STS‐95

Crystals of a human (Sea) Bence‐Jones dimer were produced in a capillary by vapor diffusion under microgravity conditions in the 9 day US Space Shuttle Mission STS‐95. In comparison to ground‐based experiments, nucleation was facile and spontaneous in space. Appearance of a very large (8 × 1.6 × 1.0 mm) crystal in a short time period is a strong endorsement for the use of microgravity to produce crystals sufficiently large for neutron diffraction studies. The Sea dimer crystallized in the orthorhombic space group P212121, with a = 48.9 Å, b = 85.2 Å, and c = 114.0 Å. The crystals grown in microgravity exhibited significantly lower mosaicities than those of ground‐based crystals and the X‐ray diffraction data had a lower overall B factor. Three‐dimensional structures determined by X‐ray analysis at two temperatures (100 and 293 K) were indistinguishable from those obtained from ground‐based crystals. However, both the crystallographic R factor and the free R factor were slightly lower in the models derived from crystals produced in microgravity. The major difference between the two crystal growth systems is a lack of convection and sedimentation in a microgravity environment. This environment resulted in the growth of much larger, higher‐quality crystals of the Sea Bence‐Jones protein. Structurally, heretofore unrecognized grooves on the external surfaces of the Sea and other immunoglobulin‐derived fragments are regular features and may offer supplementary binding regions for super antigens and other elongated ligands in the bloodstream and perivascular tissues. Copyright © 2003 John Wiley & Sons, Ltd.