To ask a potentially daft question - but why do you need to reduce the salt? You say you are able to purify it, and that it behaves on gel filtration - but only starts misbehaving when you dialyse, and the NaCl is below 100 mM.
We've crystallised many proteins, particularly DNA-binding proteins with high pI, in high salt concentrations - even up to 1M. Tony. Sent from my iPhone On 22 Apr 2013, at 23:36, "Pascal Egea" <pas...@msg.ucsf.edu<mailto:pas...@msg.ucsf.edu>> wrote: Dear All, I am presently faced with a peculiar case in the lab. We are expressing a protein in E. coli and we are able to express it as a fusion protein without problems . Fusion cleavage goes well and the final product looks homogenous by size-exclusion chromatography with the expected molecular weight. There are no signs of aggregation. However when we lower the salt concentration by dialysis then the protein forms a gel. transparent , optically clear, with no fluffy material (in the cold room). Gelification seems to occur when we lower the concentration below 100 mM NaCl. This protein has a fairly high pI (~9.0). Attempts to reverse the process by gentle heating or salt addition have been so far unsuccessful. It is not a thermophilic protein. We have not been able to obtain crystals so far. Has anyone already observed this kind of behavior and/or have any suggestions? Many thanks in advance . -- Pascal F. Egea, PhD Assistant Professor UCLA, David Geffen School of Medicine Department of Biological Chemistry Boyer Hall room 356 611 Charles E Young Drive East Los Angeles CA 90095 office (310)-983-3515<tel:%28310%29-983-3515> lab (310)-983-3516<tel:%28310%29-983-3516> email pe...@mednet.ucla.edu<mailto:pe...@mednet.ucla.edu>
