Hi, I have a protein that shows high and low MW peaks on gel filtration (which run at the same MW on SDS-PAGE). There is a slow equilibrium because rerunning the individual peaks on gel filtration a couple days later shows both peaks. The higher MW peak is ~2 orders of magnitude more dominant...the lower MW peak is not yielding much. However, as nature would have it I've only gotten the lower MW peak fractions to crystallize, and only when the affinity tag is clipped (the higher MW species is resistant to clipping). I would like to do something to shift the equilibrium towards the lower MW species. So far, I've tried (without success or clues for success) changing pH, increasing NaCl from 200 to 600mM, adding glycerol to 12%. Things that I've seen in papers but have not yet tried are temperature jumps, other salts, limited Gu/urea, Arg/glu, dioxane, limited SDS/triton.
Any suggestions are greatly appreciated, thanks very much, Mike
