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Re: [ccp4bb]: summary of sulphate binding at ATP binding sites

Hi y'all,

My 2 cents: sometimes, ATP (or any other charged ligand) won't bind to a protein if the ionic strength is high. This is due to the Debye-Huckel shielding effect and has nothing to do with the relative affinities of sulfate (NOT sulphate !!!!!) vs. ATP as any other salt would result in the same effect. I know of cases where ATP binding is reduced at fairly moderate ionic strengths already. One can easily check this by doing ATP binding studies with varying ionic strength.

Pre-forming the complex, then crystallizing it and hoping that the ATP doesn't come out, seems to be a good try.


I am trying to get cocrystals with ATP bound in the active
site. But the electron density maps show no evidence of ATP binding. I
have ~200mM ammonium sulphate, PEG and 4mM ATP in the crystallization
conditions and most probably ammonium sulphate competes with the ATP,
preventing its binding.

Mischa Machius, PhD
Assistant Professor
UT Southwestern Medical Center at Dallas
5323 Harry Hines Blvd.; Y4.330A
Dallas, TX 75390-9038; U.S.A.
Tel: +1 214 648 9760
Fax: +1 214 648 8954