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 100-200µM in buffer and
are
soluble in DMSO only up to 50mM.
Many thanks for your time,
Leo James
-- Dr George Kontopidis, Structural Biochemistry Group, ICMB, 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 g.kontopidis@ed.ac.uk