Hi Guangyu, I think it's not as straightforward as comparing d/p ratios, that is only one of several factors that influences precision. Another important factor would be the overall level of thermal motion & disorder which will most likely be significantly higher in the 3.6A 80% case; after all that's probably the reason that it only diffracts to 3.6A!
All things considered I would go for the 3A form. Cheers -- Ian On 15 March 2013 00:27, Guangyu Zhu <g...@hwi.buffalo.edu> wrote: > 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? >
