Interesting idea. The only caveat that springs to mind is that the more
useful anions (e.g., iodide and bromide) are on the chaotropic end of
the Hofmeister series and may potentially destabilize protein structure
or protein-protein interactions, which might complicate
co-crystallization starting from known conditions, especially at higher
concentrations of anion. Alternate cations may be less problematic.
Cheers,
_______________________________________
Roger S. Rowlett
Gordon & Dorothy Kline Professor
Department of Chemistry
Colgate University
13 Oak Drive
Hamilton, NY 13346
tel: (315)-228-7245
ofc: (315)-228-7395
fax: (315)-228-7935
email: rrowl...@colgate.edu
On 5/3/2012 11:29 AM, Jacob Keller wrote:
I have wondered for a long time now why it is not standard practice
for all crystallization protein stocks to contain either Br- or I-
ions instead of Cl-, even for cationic buffers like TRIS, which could
be titrated with HBr or HI to get in the 10+ mM range. Also, one could
use Cs or Rb for the cations (and titrate anionic buffers with the
respective hydroxides). What's there to lose? The gain is obviously
the possible anomalous signal (always helpful), and one might pick up
additional interesting and possibly physiologically-relevant halide or
alkali metal sites. Seems that structural genomics people might
standardize this into the pipeline as well, and thereby potentially
cut out SeMet protein production in many if not most cases.
JPK
On Thu, May 3, 2012 at 9:05 AM, Jan Abendroth <jan.abendr...@gmail.com
<mailto:jan.abendr...@gmail.com>> wrote:
Hi Rajesh,
it can be a bit all over the place:
For quick soaks, we typically use 500mM-1000mM. A good starting
point might be to simply replace the NaCl concentration in your
protein buffer. By some serendipity we also managed to solve a
structure by I/S SAD after a 1mM NaI soak. One iodide had found
its way into a nice binding pocket.
For co-crystallization, mostly 200mM should be fine.
Another approach could be to supplement your cryo buffer with
iodide, replacing NaCl. NaI is highly soluble in ethylene glycol.
Also see here: http://www.ncbi.nlm.nih.gov/pubmed/21359836
Good luck!
Cheers,
Jan
--
Jan Abendroth
Emerald Bio
Seattle / Bainbridge Island WA, USA
home: Jan.Abendroth_at_gmail.com <http://Jan.Abendroth_at_gmail.com>
work: JAbendroth_at_embios.com
http://www.emeraldbiostructures.com
On May 3, 2012, at 6:51 AM, Rajesh Kumar wrote:
Dear All,
I have very thin crystals but diffracting. I was not able to
handle them easily for iodide soak. I always lost the crystals
during manipulation and other big crystals obtained after
seeding doesn't even give any diffraction. I tried for
co-crystallizing with NaI. The crystals appear only up to 20 mM
in 1:2 (3ul drop of 1 ul protein and 2ul reservoir).
Is this concentration of iodide is enough for SAD data ( if it
had good incorporation) ?
I appreciate your help.
Thanks
Rajesh
--
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
email: j-kell...@northwestern.edu <mailto:j-kell...@northwestern.edu>
*******************************************
