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>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 > 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 *******************************************
