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[log in to unmask]" type="cite">Hi all,
I solved a structure and the refinement is close to complete. However, some residual density puzzles me.
The SG is P212121, and the c is 84.8 Å. Along c, in several small but not all regions, there are some layered, alternately appeared positive and negative residual density pieces (c is the norm of these plane-like pieces; 3-sigma contour for pos and neg difference densities). The distance between the neighboring positive pieces is measured to be ~2.1 Å, corresponding to ~1/40 *c. In one of such region, there is an indole ring of Trp that is approximately parallel to the plane-like residual density pieces (attached figure). In two other regions, there are Leu or else but not ring structure.
The data is complete to 1.9 Å. Reflection check did not show any special imcompleteness (ice ring loss, wedge loss, other resolution bin loss, etc). It looks like to me that there is a systematic loss of information which made it is specially sensitive to ~2.1 Å reflections (especially those along c*). It does not look like to me to be radiation damage. Crystal was needle and showed somehow polarized (but never serious) diffraction pattern along c*.
Attached is a piece of map with the above-mentioned Trp included. I would like to know if some one also met something like this before. Thanks for any comments.Lijun LiuCardiovascular Research Institute
University of California, San Francisco
1700 4th Street, Box 2532
San Francisco, CA 94158
Phone: (415)514-2836