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Have you done both experiments at the same temperature? If cryo - have you used the same cryoprotectant? same ionic strength? Did mutations cause changes in the surface charge distribution/hydrophobic/hydrophilic/ pi...pi interactions - if yes how it can effect quaternary structure of native. Do mutations in the model of that crystal and take a close look at the interfaces Look at Acta Cryst. 2006, D62, 766- to see discussion about effect of freezing In general if it is an external flexible loop I would be neither surprised nor worried, if different in the "rigid" core you need to seek explanation. Withdrawal/addition of water molecules causing tautomeric changes in Pro (from trans to cis peptide?) and as a result a shift of some fragment? It is known to happen and can move a domain. Good luck - ESJ ________________________________________________________________________________ Dr. Ewa Skrzypczak-Jankun Associate Professor University of Toledo e-mail: [log in to unmask] <mailto:[log in to unmask]> Health Science Campus Mail Stop#1091 http://golemxiv.dh.meduohio.edu/~ewa Department of Urology Dowling Hall r. 2257 3000 Arlington Ave. phone 419 383 5414 Toledo OH 43614 fax 419 383 3785 _________________________________________________________________________________ ________________________________ From: CCP4 bulletin board on behalf of Chavas Leo Sent: Fri 2/8/2008 1:49 PM To: [log in to unmask] Subject: Re: [ccp4bb] Different chains in the dimer Dear Yang, Thanks for the reply. Both are P21. Point mutant. MR solved the mutant using native as a model. What about the crystal contacts of the region that changed then? Is it different in "native" and "mutant" forms? Both space groups are the same, but what about the cell dimensions? Again, the packing here might be of importance. Have a look at the neighboring molecules and how the act on the varying region. Also, how different is this region? 1 angstrom? 10 angstrom? BTW, what does HTH mean? I don't know myself... everybody is using it, so I'm using it as well :) H(ope)T(his)H(elps). Kind regards. Leo ------------------------------------------------------------ Chavas Leonard, Ph.D. Research Associate ------------------------------------------------------------ Faculty of Life Sciences The University of Manchester The Michael Smith Building Oxford Road Manchester Lancashire M13 9PT ------------------------------------------------------------ Tel: +44(0)161-275-1586 e-mail: [log in to unmask]