Try adjusting the pH close to the pI to reduce solubility.
> From: Yvonne Leduc <[log in to unmask]>
> Reply-To: <[log in to unmask]>
> Date: Tue, 7 Aug 2007 10:17:18 -0600
> To: <[log in to unmask]>
> Subject: [ccp4bb] highly soluble proteins
>
> Our lab is trying to crystallize a highly soluble (100+ mg/ml) protein
> with a molecular weight of 35 kd.
>
> The protein was screened against 1536 conditions at 20 mg/mL. Most drops
> were either clear or produced "bubbles" (often oily looking). The few
> that had precipitate contained high concentrations of K3PO4, cobalt, or
> zinc. We have tried repeating some of the bubble conditions at 100+
> mg/mL and are still getting clear drops or bubbles.
>
> Is there something about highly soluble proteins and/or secreted
> proteins and/or proteins with unusual portions of their sequence that
> needs to be considered in order to successfully crystallize it?
>
> I am considering trying "salting out" using dialysis, and also adding
> ligands/inhibitors. The protein is in 50 mM NaCl plus 50 mM buffer.
>
> I welcome thoughts and suggestions on crystallization ideas,
> publications, etc.
>
> Thank you
>
> Yvonne
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