Please note that TCEP decomposes and one of the decomposition products is phosphate. Enough TCEP and you might have Zinc Phosphate crystals which can sometimes look very odd and protein looking.
Artem _____ From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Jennifer Han-Chun Tsai Sent: Thursday, September 25, 2008 6:18 PM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] losing zinc during crystallization I don't know if anyone had experience of TCEP inducing zinc acetate to precipitate. This paper mentioned this. The Crystal Structure of the Olfactory Marker Protein at 2.3 Å Resolution Paul C. Smith, Stuart Firestein and John F. Hunt Journal of <http://www.sciencedirect.com/science/journal/00222836> Molecular Biology Volume <http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%2368 99%232002%23996809996%23319471%23FLA%23&_cdi=6899&_pubType=J&view=c&_auth=y& _acct=C000049198&_version=1&_urlVersion=0&_userid=952835&md5=2d1212952cf958e 128dad1358783edf4> 319, Issue 3, 7 June 2002, Pages 807-821 I saw if protein sample containing TCEP would either form precipitation or weird and rounded shape of small molecule crystal but not salt. I have tried to crush that rounded shape crystal. It's quite soft, very similar to the way protein crystals got crushed. Does anyone have this experience? Or actually this kind precipitation could get nice crystal after optimization? Thanks, Jennifer Tsai On Thu, Sep 25, 2008 at 4:53 PM, Eric <[EMAIL PROTECTED]> wrote: We had a zinc-finger containing protein that we were soaking with different heavy atom compounds. It turns out KAu(CN)2 provided the best diffraction of several soaks. We found out it was because the gold had replaced the zinc ion and was coordinated by the Cys and His's. The lab nickednamed the protein Goldfinger! Although we didn't have the problem with disulfides, perhaps a similar gold soak might help if you tried to crystallize the protein in the presence of TCEP as well. HTH ----- Original Message ----- From: "Sue Roberts" <[EMAIL PROTECTED]> To: <CCP4BB@JISCMAIL.AC.UK> Sent: Thursday, September 25, 2008 4:35 PM Subject: losing zinc during crystallization Hello Everyone I've been trying to crystallize a zinc-containing enzyme for what seems to me to be an eternity. The protein contains stoichiometric zinc (1 zinc/ protein monomer) when isolated and the zinc is required for activity. Each crystal we've obtained has lost the zinc and contains a disulfide bond between two cysteine residues that should be zinc ligands (based on structures of similar proteins). We've tried crystalizing in the presence of reducing agents, crystallizing with substrate analogs, and supplementing the crystallization drops with zinc with no success (and combinations of these approaches). We've obtained a variety of crystals and determined structures, but none contain any zinc. Attempts to insert zinc into the crystal (zinc + reducting agent or zinc alone) have not been successful. Does anyone have any tricks to suggest that might help? Thanks in advance. Sue Dr. Sue A. Roberts Biochemistry & Molecular Biophysics University of Arizona 520 621 8171 [EMAIL PROTECTED]
