Is the dimer perhaps the natural state, and are the high oligomers non-specific aggregation?

That would be my first guess, knowing nothing about the protein you are working on.

If you are absolutely certain that the protein should be a monomer, do you have any free cys residues you could mutate or reduce with TCEP to split a disulphide linked dimer?

On 27 Feb 2014 07:57, "Tom Wong" <[log in to unmask]> wrote:

Hello everyone!

I have run into a problem in a 55kD recombinant human protein crystallization (expressed in E.Coil). The purity is pretty good. However, it behaves as high oligomers in the buffer with 300mM NaCl and behaves as dimers with a little high oligomers in the buffer with 2000mM (2M) NaCl.

I have already performed several screenings and tried several types of buffer, salt or different pHs, etc. Only very small crystals could be detected in the dimer drops. High oligomers seem could not be crystallized under various of conditions.

Has anyone ever met the same problem? Could anyone give me some suggestions?

Thanks very much!

Cheers

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Tom Wong

Structural Lab

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