Dear Guangyu, 80% solvent is an awful lot. The first thing I would do is to check that there is not another protein molecule hiding somewhere in the asymmetric unit. What I usually do in these cases is to set a very large map radius (say 40-60 Å) and look at the complete solvent region to see if there are regions which are significantly more "noisy". I would also check that the crystal packing makes sense, e.g. continuous contacts in all three dimensions and no layers without any protein contacts.
Of course that best results are obtained by building and refining both crystal forms and cross-checking the results from one crystal form in the other crystal form. Having said that, I have had some amazingly clear and unbiased electron density maps from low-resolution, high solvent crystals. It were molecular replacement structures, but due to the very strong solvent flattening effect, the phases looked like experimental ones. If your low-resolution structure genuinly has 80% solvent, I would be tempted to start building in that map. Best, Herman ________________________________ From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Guangyu Zhu Sent: Friday, March 15, 2013 1:28 AM To: CCP4BB@JISCMAIL.AC.UK Subject: [ccp4bb] Resolution and data/parameter ratio, which one is more important? I have this question. For exmaple, a protein could be crystallized in two crystal forms. Two crystal form have same space group, and 1 molecule/asymm. One crystal form diffracts to 3A with 50% solvent; and the other diffracts to 3.6A with 80% solvent. The cell volume of 3.6A crystal must be 5/2=2.5 times larger because of higher solvent content. If both data collecte to same completeness (say 100%), 3.6A data actually have higher data/parameter ratio, 5/2/(3.6/3)**3= 1.45 times to 3A data. For refinement, better data/parameter should give more accurate structure, ie. 3.6A data is better. But higher resolution should give a better resolved electron density map. So which crystal form really give a better (more reliable and accurate) protein structure?
