>Another theory is that trace amounts of Ni may leech off the column during
>purification and coordinate with multiple His-tags on the pure protein,
>causing them to aggregate.
For sure. We had a case where a protein would precipitate after post-Ni-NTA
dialysis. The precipitate would go back into solution if resuspended in the
presence of imidazole or EDTA/EGTA. Inclusion of a bit of EDTA into
fractions and dialysis solution completely eliminated precipitation.
Dima
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