Dear Jerry,

One way I can think of would be to try the magical polymer NV-10 sold by Novexin (UK). It does actually work very well for proteins with low solubility. You’d add a few mg/ml of polymer to each protein solution, mix the two and see what happens. This polymer has already saved several of my poorly soluble proteins and I hear from others that it worked well for them, too.

If you’re desperate – I would recommend rational surface mutagenesis. We, and others, have designed surface mutants with greatly improved solubility J Or fuse with something nice and soluble.

Artem

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From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Jerry McCully
Sent: Wednesday, December 12, 2007 3:31 PM
To: [log in to unmask]
Subject: [ccp4bb] protein precipitated when they formed a complex

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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