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Re: [ccp4bb]: Co-crystallisation with hydrophobic ligands



 
Dear Leo,

The solubility is not really a problem as far as the Kd (dissociation constant) is very low.

Scenario 1 Kd is small:
***********************

In a hypothetical situation in which protein concentration (usually in crystallization drop) is 1mM and addition of ligand
is 1.01mM and  Kd < 100nM,
more than 90% of the protein will be in complexed form with ligand even if the solubility of ligand is 10 microM .

Scenario 2 Kd is high:
**********************

Now if the Kd (or Ki) is not so small then you need high concentration as Gitay Krygen suggested (around Ki x 10).
I would suggest to find a solvent (e.g. EtoH, MeOH, DMSO) in which the ligand is more soluble and make the highest
ratio of buffer/solvent in which the protein can stand (i will suggest less than 5% w/v) dissolve the ligand there and use
that solution for co-crystallization.
 
 

Leo James wrote:

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  Hi,

  Im wondering if anyone has any clever strategies for co-crystallising
  complexes with very hydrophobic ligands.  The ligands I am using are
  insoluble at concentrations upwards of 100-200ÁM in buffer and are
  soluble in DMSO only up to 50mM.

  Many thanks for your time,

  Leo James
 
 

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Dr George Kontopidis,
Structural Biochemistry Group,
ICMB,
The University of Edinburgh,
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