index/CrySis/Research/Crystal Quality
Background Diffraction

Crystal Quality


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Protein Quality

It is imperative for successful structure determination that the crystal yields an acceptable diffraction pattern. If the protein crystal has impurities, or if it is misshapen, destructive interference by the X-rays will blur the diffraction pattern. In order to properly place the amino acid groups, a clear diffraction pattern is necessary. There is a threshold to the amount of noise that is acceptable for a diffraction pattern. Usually the quality of the diffraction must be evaluated by an expert, however, CrySis can do this automatically.


The image on the left is an example of an exemplary diffraction pattern, the one on the right is an unusable diffraction pattern. Viable protein diffraction patterns have a number of unique properties. They have numerous extremely intense peaks scattered around the image; poor diffraction patterns have few meaningful peaks. Peaks are arranged in a different, but meaningful order for every diffraction pattern. The location of the peaks does not differentiate a viable crystal from a poor one, but the distribution of peaks does. The intensity of the peaks in a viable crystal is at its maximum in the center of the image, and slowly falls off towards the outside; the intensity gradient in a poor scatter is very steep.