Dear Skkannu,
since citrate is (a) necessary for crystal growth and stability and (b)
blocks the active site I am afraid you will have to find a completely
different crystal form. This means start screening all over again for
crystallization conditions of your enzyme in the presence of a
sufficiently large amount of ligand. And make sure your ligand is not
prcessed by the enzyme.
Best regards,
Herman
________________________________
From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On
Behalf Of Samy kannu
Sent: Thursday, June 11, 2009 4:40 PM
To: CCP4BB@JISCMAIL.AC.UK
Subject: [ccp4bb] citrate blocks the active site
Dear all,
One of my enzymes crystallized in 0.1 M citric acid pH
3.5 and 25% PEK 3350. The structure solution reveals, citrate molecule
is occupying the active site.
Moreover citrate mediates the dimer formation.
I tried crystallization in the same condition with
ligand using soaking with different concentrations of ligands and lower
concentration of citric acid (below 0.5 M of citric acid, crystals are
broken). Cocrystallization also tried.
I collected several data sets with these combinations.
The Structure solutions from all these data sets give
only citrate complex.
I found crystals only in citrate condition.
Any suggestions !!
Thanks.
Skkannu
