Characteristics of dislocations in protein crystals

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The object of this research is to understand characteristics of dislocations in protein crystals. We have attacked the problems by means of two ways. One is to observe clear images of dislocations and to determine the Burgers vectors by synchrotron X-ray topography. The other is to estimate the elastic energy of dislocations and the mechanical strength by an ultrasonic pulse echo method and an indentation method.Crystal defects, especially dislocations, in hen egg-white lysozyme crystals that are a typical protein crystal that have - multiple polymorphisms, for example tetragonal, orthorhombic and monoclinic forms were investigated by means of synchrotron white and monoclinic-beam X-ray topography. The observed topographic images of dislocations were much clearer compared to those of any protein crystals that have been reported so far. It was demonstrated that millimeter-size crystals larger than extinction length for X-ray topographic reflections are required to obtain clear images, t … More hat is, direct images for protein crystals. In addition the weak beam technique was found to be useful for obtaining clear images. Straight, curved and loop-type dislocations were clearly resolved on the topographs. This shows that dislocations observed in common inorganic and organic with small molecules can also be introduced even in protein crystals. The shapes and distributions of dislocations strongly depended on the crystal polymorphisms. This suggests that the growth mechanisms in the different crystal forms studied could differ. Therefore, X -ray topography provides a useful tool for the characterization of protein crystal dislocations.We have succeeded the measurement of all components of elastic constants in hen egg-white lysozyme crystals using an ultrasonic pulse echo method. The measurements of the sound velocity were performed using (110) , (101) and (001) crystal surfaces. Consequently, all the six elastic constants of the dehydrated tetragonal HEW lysozyme crystals were determined to be C_<11>= C_<22>= 12.44 GPa, C_<12> =7.03 GPa, C_<13>= C_<28> =8.36 GPa, C_<88> =12.79 GPa, C_<44>=C_<55> =2.97 Gpa and C_<66>=2.63 Gpa, respectively.In addition, Mechanical properties of high quality tetragonal hen egg-white lysozyme single crystals, which are one of protein crystals were investigated by the indentation method. The indentation marks were clearly observed on the crystal surface and no elastic recovery of them occurred. The value of the micro-Vickers hardness in wet condition was estimated to be about 20 MPa at room temperature. The hardness greatly depended on the amount of water (intra-crystalline water) contained in the crystals. The hardness increased with increasing evaporation time to air at room temperature. It reached the maximum at about 260 MPa, which is 20 times as much as that in the wet condition. The origin of such a change in hardness was explained in terms of the dislocation mechanisms in lysozyme single crystals. Less