| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1998: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1997: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Research Abstract |
The dynamic property of protein is quite important as well as its 3D structure for understanding its function. Therefore, we attempted to clarify the protein dynamics by means of X-ray structural analyses, focusing on B.ccli dihydrofolate reductase (DHFR). As the crystallization condition of DHFR was not registered on BMCD database and the method by Kraut's group was not reproducible, we consumed long time for its crystallization. First, we examined the stability of the obtained crystal for exposing the white X-ray in the time-resolved Laue experiment. In general, protein crystals decay by the white X-ray which contains wide range of wavelength, but we could obtain an excellent Laue pattern which is suitable enough for the dynamic studies. The Laue dynamic study requires not only X-ray crystallography but also the control of chemical reactions and physical characterization. Then, we studied the structure-flexibility relationship of DHFR before the Laue experiment. Vie made some DHFR mu
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tants at site 67, which locates on one of the flexible loops, and determined their crystal structure. On the other hand, we measured the adiabatic compressibility of the mutants at sites 67, 121, and 145, which is dominantly determined by the internal cavity in the protein molecule. Interestingly, we could find out the good correlation between the compressibility and the cavity volume derived from the crystal structures. Moreover, the distribution of the cavities in the protein molecule were found to be quite different with the mutants. On the other hand, there was no additivity in the function and stability of double mutants at sites 121 and 67 which separates about 28 A, suggesting the existence of long-distance interaction. Thus, the difference in the cavity distribution of mutants can be explained by such long-distance effects. As temperature is quite important factor for the flexibility, we applied cryo-X-ray measurement for G67A mutant at 130 and 190K.The B-factor decreased by cooling, but the extent was quite site-specific. Especially, the loop regions on the molecular surface and helix alpha C, which participates in the substrate binding, showed quite large decrease in flexibility. These structure and flexibility relationships will present important information for planning the Laue experiments. Less
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