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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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  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

Dr George Kontopidis,
Structural Biochemistry Group,
The University of Edinburgh,
Swann Building, King's Buildings,
Mayfield Road, 
Edinburgh EH9 3JR, Scotland

Tel: +44-(0)131-650-7046/7051: Fax: +44-(0)131-650-7055