AUTOMATIC CENTERING OF PROTEIN CRYSTALS USING X-RAYS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In order to fully automate the crystal screening process, methods to automatically align protein crystals to the x-ray beam were refined. The approaches focus on using average I/Sig(I) from low-dose diffraction images taken at various crystal positions in the x-ray beam. These images are analyzed using the image analysis program, DISTL, in order to estimate I/Sig(I), and based on this analysis, a range of parameters are examined and refined in specific algorithms for optimal crystal alignment, determining and using the maximum diffracting power of the crystal rather than the optical center. During the grant year, the algorithm for centering samples was thouroughly tested on each macromolecular crystallography beam line. These tests revealed that different beam characteristics necessitated further refinement of the algorithms, which was accomplished through the development of auto-alignment of the beam to the phi axis of the goniometer.