Hello Jenny, 0.2 Rmerge may be an indication of incorrectly assigned SG or perhaps a misindexing by one, etc. Check what happens if you reprocess in P4.
For a 10kDa protein, your unit cell is kind of large - depending of course on the symmetry, the higher obviusly the better. I would bet that you have pretty high solvent content - nothing scientific about this prediction, merely personal experience with several small proteins that crystallized in high-symmetry SG and had >80% solvent. What you may want to do is to very carefully study your cryo. When we were working on a structure of FliS-FliC complex(http://www.xtals.org/pdfs/FliC_FliS.pdf), the only way to freeze the crystals correctly was to increase the concentration of sulfate ion in the cryoprotectant. It later turned out that we had a sulfate ion bridging a symmetry threefold, and in low sulfate the ion would leave, resultuing in disorder in the crystals. Ultimately, if you've already tried all the 'standard' tricks, such as additives, glycerol/eg in the condition, replacing NaCl with an exotic salt such as KCl, CsCl, RbCl, and so forth - perhaps you may want to consider adjusting the surface of the protein. I would be glad to help you with that. Artem
