[Protein-analysis] Re: protein complex precipitation

[Dr Engelbert Buxbaum]

Am 19.04.2007, 11:39 Uhr, schrieb YOGESHA. S. D <yogeshasd from yahoo.co.in>:

> When I subjected the pooled fraction for GST cleavage with protease at  
> 15 degrees the protein precipitates.

This can happen if your proteins are hydrophobic. They are kept in  
solution by the hydrophilic tag, once that is removed they precipitate.  
One obvious solution is to use the protein with the tag still on.

If that is not possible you can use a mild detergent to increase the  
solubility of the protein, which detergent can do that without  
denaturation of the protein can be found out only by trial end error.  
Triton, alkyl-glycosides or alkyl-PEG tend to work more often than others.

Urea can also solubilise proteins, but of course that destroys the  
secondary structure.