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PubMed2000

Redox-Induced "Zipper" Action in Rb(2)Bi(4)Se(7) and Cs(2)Bi(4)Se(7): Coupling of Slabs to a Three-Dimensional Framework through Single-Crystal to Single-Crystal Conversion Financial support from the Office of Naval Research (contract No. N00014-98-1-0443) is gratefully acknowledged. The work made use of the SEM facilities of the Center for Electron Optics at Michigan State University (MSU). The Siemens SMART CCD diffractometer at MSU was purchased with funds from the National Science Foundation (CHE-9634638). We thank Victor G. Young and the X-ray Crystallographic Laboratory of the University of Minnesota for collecting the data set of RbBi(4)Se(7).

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Journal Article↗
PubMed1995

The mechanism of protein crystal growth from lipid layers.

Two-dimensional (2D) crystals of proteins on lipid monolayers can initiate the formation of large three-dimensional (3D) crystals suitable for X-ray diffraction studies. The role of the 2D crystals in this process has not been firmly established. While it is likely that the 2D crystals serve as nuclei for epitaxial crystal growth, other mechanisms, such as non-specific nucleation induced by the high local concentration of the protein at the surface of the lipid layer, cannot be excluded. Using streptavidin as a model system, we have now firmly established that 3D crystal growth from 2D crystals on lipid layers occurs by epitaxy. We show that 2D crystals of streptavidin (space group C222) on biotinated lipid layers nucleate the growth of a 3D crystal form (space group I4I22) that possesses a structural similarity with the 2D crystal, but have no effect on the growth of 3D crystal forms (I222 and P2(1)) that are unrelated to the 2D crystal. At lower pH, a new 3D crystal form (space group P1), unrelated to the previously described 2D crystals, grew from lipid layers. This discovery initially raised concern about the validity of the epitaxial mechanism, but these concerns were alleviated with the subsequent discovery of a structurally related 2D P1 crystal that grew in similar solution conditions. Some parameters affecting epitaxial growth of both the P1 and I4I22 crystals were investigated, revealing several noteworthy features of the epitaxial growth. (1) 2D crystals are very effective nucleating agents; for instance, the P1 2D crystals can direct the growth of P1 3D crystals even under conditions that favour the growth of other crystal forms. (2) The epitaxial 3D crystal grow very rapidly and at amazingly low protein concentrations; P1 3D crystals can be grown from solutions as low as 10 microM streptavidin. (3) There is no obligate requirement for the deposition of pre-formed 2D crystals; lipid layers alone are equally effective at promoting epitaxial crystal growth.

Bacterial Proteins↗
PubMed2001

Dissolution rate of hen egg-white lysozyme crystal under microgravity.

Protein crystallization under micro gravity has been already tried many times in the United States and other countries, and it is reported that about 20% of proteins were better crystallized under microgravity than on earth. This verified that microgravity is sometimes effective in protein crystallization. However, if these procedures continued to be carried out without clarifying which processes are effective, improved development of protein crystallization cannot be expected. The most effective way to study the process is to carry out protein crystallization experiments, each elementary stage of which is clearly observed. To this end, the dissolution rate of a single crystal of hen egg-white lysozyme has been measured both under microgravity and on earth in order to study the mechanism of protein crystallization. In May 1997, we had an opportunity to have an experiment on protein crystallization with use of STS-84 space shuttle missions (the time duration of which was 210 hours). The apparatus for protein crystallization by vapor diffusion techniques was available and we have tried to use it for measurement of crystal dissolution rate under microgravity. The barrels of two syringes (20 ml x 2) were filled with unsaturated protein solutions (hen egg-white lysozyme (HEWL): 0.0wt%, 0.1wt%, 0.2wt%, 0.3wt%; NaCl 3wt% aqueous solution) and a crystal (HEWL: tetragonal form; 1 mm +/- 0.2 mm in diameter) was put on the bottom of the one syringe. Dissolution of the crystal was started by extruding the unsaturated solutions onto the syringe tip with the crystal. The crystal dissoluted in 40 ml droplets that are extruded from syringes. The temperature was kept at 20 degrees C. Just before the Space Shuttle begins returning to the earth, the protein solution was withdrawn back into the syringes by the astronaut, and the melting experiment was finished. In the one syringe the incompletely melted crystal was withdrawn as well. The solution concentration in the other syringe was measured. In the flight experiment, only the initial and final solution concentrations can be measured. In the control experiment on earth the solution concentrations in the course of dissolution were also measured. 20 undersaturated solutions (40 ml in volume) were prepared and a crystal (1 mm +/- 0.2 mm in diameter) was put in each solution. The solution concentration was measured at constant time intervals. When the crystal starts to dissolute [correction of dissolue], molecules in the crystal surface leave the crystal, the concentration around the crystal becomes high and there occurs a radial concentration gradient centered on the nucleus. Molecules diffuse along the gradient and go farther from the crystal. On earth, the concentration gradient might be disturbed by convection and the high concentration around the crystal might be disturbed more quickly than under microgravity. We might therefore expect that dissolution rate on the ground should be larger than under micro-gravity. However, our experimental results show that the expectation was not correct. What might the reason be? One possible reason is that there might be Marangoni convection effects in the apparatus for protein crystallization by vapor diffusion techniques used for the melting experiment. This effect has also been observed by Chayen et al.

Animals↗