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Hi there Thank you for the advice regarding my twin data (mostly sent off the board). Seems I didn't put enough info in the email sorry for that! The resolution is 2.6Ang. My first thought was that the crystal was a fragment of the full length protein. The crystals are undergoing mass spec (the proteins itself appears stable using DLS etc)... I did try molecular replacement in the different space groups prior to detwin with variants of my search model. Truncate for the centric moments of E show a value close to 1.5 (perfect twin is 1.5) H test for twinning close -lkh is close to 0.5 Pseudo twin fraction is given as 0.43 The unmerged data processed in p1 are selected as p21 by Pointless and P421/3 if given as unmerged in p21. Thankfully I have new crystals now... Gina -----Original Message----- From: George M. Sheldrick [mailto:[log in to unmask]] Sent: Friday, October 01, 2010 6:35 PM To: Clayton, Gina Martyn Cc: [log in to unmask] Subject: Re: [ccp4bb] Twinned data If you really have the systematic absences for P41 or P43 then you must have (at least) four molecules in the cell, twinning cannot reduce this. Since a solvent content of 16% is too low, the most likely explanation is that it is not twinned but that the protein is smaller than the one you are expecting. With an unknown sequence and no experimental phase information such as SAD or MAD, your only hope would be Arcimboldo, but that requires data to about 2A or better (you don't mention the resolution). As an even longer shot, you could search the PDB for matching cells and space groups. George Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-22582 On Fri, 1 Oct 2010, Clayton, Gina Martyn wrote: > Hi there > > Just wondering if anyone has any suggestions how I can deal, if > possible, with the following situation -. My first encounter with > twinned data... > > which initially indexed as p43/p41 cell dimensions 58.4 58.4 61 90 90 > 90. > Having seen the Matthews Coefficient for the solvent content of the unit > cell as 16% I discovered the data are merohedrally twinned with twin > fraction given as 0.1. > > I reprocessed the data as p1, p2 p21, c2221 (Rsymm etc indicates wrong > space group, Mats Coeff 16%) p4 etc. In p2 the (pseudo) twin fraction is > given as 0.43 (Mats Coeff 60% solvent 2.7 mol/ASU). > > I ran Detwin (ccp4) on the p2 p21 data with alternate operators as > indicated by Xtriage in Phenix. I have had no molecular replacement > solution i.e. Molrep rotational searches are not giving peaks and Phaser > has not found a solution (nor with alternates of the search "model"). > > Does anyone have any suggestions/best paper to consult etc based on > their experience of twinned data (aside from sort the crystals out...) > or should I "throw in the towell?" > > Thanks in advance for any information and advice > > Gina > > > > > Notice: This e-mail message, together with any attachments, contains > information of Merck & Co., Inc. (One Merck Drive, Whitehouse Station, > New Jersey, USA 08889), and/or its affiliates Direct contact information > for affiliates is available at > http://www.merck.com/contact/contacts.html) that may be confidential, > proprietary copyrighted and/or legally privileged. It is intended solely > for the use of the individual or entity named on this message. If you are > not the intended recipient, and have received this message in error, > please notify us immediately by reply e-mail and then delete it from > your system. > > Notice: This e-mail message, together with any attachments, contains information of Merck & Co., Inc. (One Merck Drive, Whitehouse Station, New Jersey, USA 08889), and/or its affiliates Direct contact information for affiliates is available at http://www.merck.com/contact/contacts.html) that may be confidential, proprietary copyrighted and/or legally privileged. It is intended solely for the use of the individual or entity named on this message. If you are not the intended recipient, and have received this message in error, please notify us immediately by reply e-mail and then delete it from your system.