Hi Jerry,
have you tried tinkering with the pH?
I have had similar situation, where two normally soluble proteins
precipitated upon mixing at pH 7.5, my "stock" buffer. Altering the pH
showed that the complex that was only soluble at pHs lower than 6.
Looking at your pIs, it strikes me that in between 6.5 and 10 is 8,
which is where most peoples "stock buffers" live - if your complex has
a pI at your current pH, then it's not going to be at its most
soluble.
Failing that, the NDSB solubising agents are worth a shot...
Hope this helps,
David.
On 12/12/2007, Jerry McCully <[log in to unmask]> wrote:
>
> Dear All,
>
> Recently I posted a question about protein induced protein
> precipitation.
> Firstly I'd like to thank many folks for their good ideas.
>
> Later on I did a titration experiment with one protein concentration
> fixed at 0.4mg/ml(about 10uM). Now it is clear that these two proteins
> stoichiometrically precipitated when they formed a 1:1 complex. The excess
> of individual proteins was just soluble in the buffer.
>
> How come these two proteins co-precipitated when they formed a complex?
>
> Does anyone know some methods to keep the complex soluble enough for
> crystallization?
>
> By the way, there is some additional information about the individual
> components. One has a pI of 6.5, and the other has a pI of 10.
>
>
> Any suggestions will be highly appreciated.
>
> Jerry McCully
>
>
>
>
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--
============================
David C. Briggs PhD
Father & Crystallographer
http://personalpages.manchester.ac.uk/staff/David.C.Briggs/
AIM ID: dbassophile
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