I hope the following might make things easier to grasp. The 3.0Angstrom diffraction resolution is basically required to resolve a protein polypeptide chain whether your protein is in an 80% solvent content unit cell or a 50% solvent content unit cell. You will have more observations in the former than in the latter to reach that goal. In the days of a single counter four circle diffractometer that was a major overhead. As has been alluded to in considerable detail in other replies solvent flattening does however give phase determination benefits and 80% is better than 50%.

John

Prof John R Helliwell DSc FInstP CPhys FRSC CChem F Soc Biol.

Chair School of Chemistry, University of Manchester, Athena Swan Team.

http://www.chemistry.manchester.ac.uk/aboutus/athena/index.html

On 15 Mar 2013, at 00:27, Guangyu Zhu <[log in to unmask]> 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?