I think what one uses will depend on what one expects to be in the structure and the resolution and the quality of their diffraction data.
I usually start with 1.8 Å resolution data in case there is chance of having disulfides. Then 1.9, then 2.4, then 2.0, then 2.6, then 2.2, then 1.85, then 1.75, …. If there are disulfides, then there is the DSUL option if the resolution of the diffraction data is not conducive to separating the individual sulfur atoms. One should also change the number of sites that SHELXD is looking for, perhaps in a systematic way. For example, one might be looking for sulfurs based on amino acid sequence, but there may be calcium, zinc, manganese, or other strong anomalous scattering atoms in the crystal that would make searching for sulfurs moot or at least problematic. Jim ________________________________ From: CCP4 bulletin board [CCP4BB@JISCMAIL.AC.UK] on behalf of Monica Mittal [monica.mitta...@gmail.com] Sent: Tuesday, April 22, 2014 3:13 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] shelxd Dear all I am naive in phasing experiments. CAn anyone please guide how to do the following: In a S-SAD for SHELXD searches, try various high-resolution cutoffs for example 2.5 to 5 Å in steps of 0.1 Å. Based on these attempts, use a high-resolution cutoff at for example 3.8 Å for substructure determination with an E min value of for example 1.6 to search for X no. of protein sulfur sites. Thanx in advance Monica
