Hi Jacob That doesn't surprise me at all, though the example you heard is probably towards the extreme end of what we've seen. We have seen individual cell parameter changes up to 10% on soaking/freezing which could easily add up to 20-30% change in cell volume. One problem with freezing is that it's almost impossible to reproduce the freezing conditions exactly (e.g. due to variations in concentrations of organic solvent, buffer, ligand, protein & in the rates of freezing), even using the same ligand, so that you can easily get variations in cell parameters just induced by freezing alone.
Note this puts a 'spanner in the works' of maintaining the same Rfree set across a series of ligand complexes (as discussed in a recent thread), because if the cell parameters change by even a few per-cent the structures become non-isomorphous, and then what you think are the same set of reflections in different datasets, actually define quite different points in the molecular transform. Since I don't believe this 'Rfree bias' exists beyond the first refinement anyway this doesn't bother me, but it should bother others who do believe that it's necessary to take extreme measures to 'shake out' such bias. Cheers -- Ian > -----Original Message----- > From: owner-ccp...@jiscmail.ac.uk [mailto:owner-ccp...@jiscmail.ac.uk] On > Behalf Of Jacob Keller > Sent: 22 October 2009 20:21 > To: CCP4BB@JISCMAIL.AC.UK > Subject: Changes in Cell Constants > > Dear Crystallographers, > > I have just returned from a seminar in which Robert Sauer said that they > saw > a change in cell volume by 25% upon soaking crystals with substrate > (ATP-gammaS). He also showed that one of the cell constants changed by > about -25 Ang from 200 Ang. I am assuming that the space group did not > change--otherwise this phenomenon would not deserve comment. I asked > whether > he could see the crystals change size under the microscope, and he said a > hard-to-interpret "yes." > > Has anybody seen such large changes in cell constants in soaks, without > cracking? If so, could you actually see the crystals shrink as the ligand > entered the crystal? > > Regards, > > Jacob Keller > > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > Dallos Laboratory > F. Searle 1-240 > 2240 Campus Drive > Evanston IL 60208 > lab: 847.491.2438 > cel: 773.608.9185 > email: j-kell...@northwestern.edu > ******************************************* Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing i.tic...@astex-therapeutics.com and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674
