Preventing protein aggregation - (Mar/22/2007 )

Hi
I have overexpressed a DNA binding protein with N-terminal 6-His. After i do a native purification in Ni column using Imidazole i find three C-terminal truncated bands in SDS-PAGE.So i planned to do Gel filtration.And for this purpose i concentrated the proteins 5mg/15ml to 5mg/ml in 20mM TrispH7.5. But the concentrated proteins got aggregated.I have planned to use the protein for crystallization.

Please suggest additives or salts or any other measures that can prevent aggregation.
Thanks in advance

Depending on what you want to do next, there's a number of different salts you can use. Phosphate is good, as is NaCl. Try NaCl to about 100 mM, or 50 to 100 mM phosphate. Ammonium sulphate is also good at low concentrations (say up to 50 mM).

Good luck!