I'm trying to characterize the 3D structure of the extracellular domain of 300 kDa of a membrane protein. A problem I'm trying to solve is the formation of aggregates when trying to visualize the protein with cryo-EM. One technique I'm using to optimize buffer conditions a thermal stability assay, which I want to use to check three different buffers over a certain pH range. I was wondering what other buffer types people have used to optimize the stability of your protein. Right now I'm working with a protein concentration of 75 ug/ml in a buffer of 10 mM HEPES, 75 mM NaCl, 1mM CaCl2 at pH 7.8.
Yours looks fine, we use HEPES 50 mM pH = 8,0, NaCl 100 mM. Just try to not add glycerol if possible (it hampers structure resolution), and keep salt concentration low. Detergents can sometimes worsen your contrast too, so keep that in mind.
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