Identification of dislocations in large tetragonal hen egg-white lysozyme crystals by synchrotron white-beam topography

Radiation-induced defects in protein crystals observed by X-ray topography

The characterization of crystal defects induced by irradiation, such as X-rays, charged particles and neutrons, is important for understanding radiation damage and the associated generation of defects. Radiation damage to protein crystals has been measured using various methods. Until now, these methods have focused on decreased diffraction intensity, volume expansion of unit cells and specific damage to side chains. Here, the direct observation of specific crystal defects, such as dislocations, induced by X-ray irradiation of protein crystals at room temperature is reported. Dislocations are induced even by low absorbed doses of X-ray irradiation. This study revealed that for the same total absorbed dose, the formation of defects appears to critically depend on the dose rate. The relationship between dislocation energy and dose energy was analyzed based on dislocation theory associated with elasticity theory for crystalline materials. This demonstration of the crystal defects induced by X-ray irradiation could help to understand the underlying mechanisms of X-ray-induced radiation damage.

Identification of grown-in dislocations in protein crystals by digital X-ray topography

X-ray topography is a useful and nondestructive method for direct observation of crystal defects in nearly perfect single crystals. The grown-in dislocations from the cross-linked seed crystal in tetragonal hen egg-white lysozyme crystals were successfully characterized by digital X-ray topography. Digital X-ray topographs with various reflections were easily obtained by reconstruction of sequential rocking-curve images. The Burgers vector of the dislocation is different from those reported previously. Interestingly, one of the dislocations had a bent shape. The preferred direction of the dislocation line was analysed by the estimated dislocation energy based on the dislocation theory. The dislocation energy can be estimated by the dislocation theory even in protein crystals composed of macromolecules.

Digital topography with an X-ray CCD camera for characterizing perfection in protein crystals

Digital X-ray topography using an X-ray CCD camera and conventional X-ray topography using X-ray film were used to investigate tetragonal hen egg-white lysozyme (HEWL) crystals. Previously, clear dislocation images of protein crystals were mainly obtained by film methods. Earlier studies of HEWL crystals using an X-ray CCD camera mainly revealed domain structures. In the present study, dislocation images of the same HEWL crystal have been obtained by using conventional X-ray film and a digital X-ray CCD camera. The results demonstrate that digital topography using an X-ray CCD camera is an effective method for characterizing protein crystals. A series of digital topographic images were analyzed by the method developed by Lovelace, Murphy, Pahl, Brister & Borgstahl [J. Appl. Cryst.(2006),39, 425–432]. Sub-peaks and peak broadening originating from dislocations in local rocking curves were observed. Moreover, the crystal perfection was evaluated by mapping the angular positions of the maximums and the full widths at half-maximum of local rocking curves.

Elastic constants in tetragonal hen egg-white lysozyme crystals containing large amount of water

Transverse sound velocity of cross-linked tetragonal hen egg-white (HEW) lysozyme crystals containing large amount of water in the crystal was measured using ultrasonic pulse-echo method. All elastic constants of cross-linked crystals were observed to be C11=C22=5.50 GPa, C12=4.33 GPa, C13=C23=3.94 GPa, C33=5.22 GPa, C44=C55=0.68 GPa, and C66=0.84 GPa, respectively. We found that the elastic constants of the cross-linked crystals are identical to those of the intrinsic ones without cross-linking. Moreover, we found that tetragonal HEW lysozyme crystals that enclose large amount of water show decreased elastic constants (softening). In particular, the shear elastic constants C44=C55 and C66 showed more softening effect comparing with other elastic components.

Observation of all the components of elastic constants using tetragonal hen egg-white lysozyme crystals dehydrated at 42% relative humidity

Success in measuring transverse sound velocity allowed us to determine, for the first time, all six elastic constants of a protein crystal. An ultrasonic pulse-echo method was used to perform sound velocity measurements on tetragonal hen egg-white (HEW) lysozyme crystals that were partially dehydrated at 42% relative humidity. The measurements were performed using the (110), (101), and (001) crystallographic faces. Thus, all six elastic constants of the dehydrated tetragonal HEW lysozyme crystals were determined: C11=C22=12.44 GPa, C12=7.03 GPa, C13=C23=8.36 GPa, C33=12.79 GPa, C44=C55=2.97 GPa, and C66=2.63 GPa. In addition, for the hydrated crystals, the longitudinal sound velocities along the [110] direction and the direction normal to the (101) face were measured. From these results, all the components of elastic constants in the hydrated crystals were extrapolated.

Effect of intracrystalline water on longitudinal sound velocity in tetragonal hen-egg-white lysozyme crystals

Longitudinal sound velocity of tetragonal hen-egg-white (HEW) lysozyme crystals was measured during air drying by ultrasonic pulseecho method. The sound velocity increases with exposure to open air and approaches a constant value. The maximum value is approximately 2900 m/s that is about 1.6 times as much as that of original one before drying. In addition, the sound velocity clearly recovers to original one after immersing the dried crystal in solution. Therefore, the sound velocity in tetragonal HEW lysozyme crystals can be reversibly changed due to dehydration and rehydration. These changes in sound velocity are discussed in the light of water-mediated intramolecular and intermolecular interactions in the crystals.