Dear All, I have a MAD dataset at 4Å and shelxD can find clear-cut 10 solutions (my protein has 12 methionines). I ran autosharp to refine them followed by density modification. After density modification, I ran solvent flattening. Then I calculated the anomalous map using the phase from sharp and the electron density map from solvent flattening. The anomalous map shows the density around these 10 selenium sites are clear and round. However, the density map from solvent flattening showed that only 4 selenium sites have clear and round density. The density around these 4 sites clearly showed beautiful helices. surprisingly, other 6 selenium sites have poor density or no density at all. The electron density around them is not very good and the predicted helical density is flat. I check the electron density before I ran solvent flattening. The result is same. I am quite confused about the big difference from these two maps. I also try SnB to find the selenium sites. The solutions are same as those from ShelxD. But How to explain the poor density around the selenium sites in the density modification map? Is there any problem with my selenium sites? Any suggestion from crystallographic experts? Thanks.
Mousheng Wu, PhD Center for Membrane Biology Department of Biochemistry and Molecular Biology The University of Texas Medical School at Houston 6431 Fannin Street, Houston, TX, USA, 77030
