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*To*: Titia Sixma <sixma@nki.nl>, ccp4bb@dl.ac.uk*Subject*: Re: twinning*From*: Roman Hillig <roman.hillig@charite.de>*Date*: Fri, 14 Jan 2000 16:04:05 +0100*References*: <Pine.GSO.4.20.0001141427010.21365-100000@Hermes.nki.nl>*Sender*: owner-ccp4bb@dl.ac.uk

*** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.dl.ac.uk/CCP/CCP4/main.html *** Dear Titia I solved a structure from partially hemihedrally twinned xtals by MIRAS. (Published in Hillig, R.C., Renault, L., Vetter, I.R., Drell, T., Wittinghofer, A., and Becker, J. (1999). The crystal structure of rna1p: A new fold for a GTPase-activating protein. Molecular Cell. 3, 781-791.) I know of one more MIR-twin-paper, but with very low twin fraction. And with a special case, NCS axis close to crystallographic axis, therefore using a differnt way to calculate twin fraction alpha: Forst, D., Welte, W., Wacker, T., and Diederichs, K. (1998). Structure of the sucrose-specific porin scry from salmonella typhimurium and its complex with sucrose. Nature Structural Biology 5, 37-46. In my case, we managed to find a relatively low twinned native. But among the derivatives, a highly twinned one (24%) gave the by far best phases. These were very much improved by detwinning the data. So in the end, partial hemihedral twinning should not hinder MIR structure determination, given that your data are not twinned higher than 25-30 %. (Data from a crystal with a twin fractions of 33% were not correctable any more.) In my case, the space group was I41, so I am now familiar with twinning in tetragonal space groups. And my little program so far is just dealing with tetragonal symmetry. But there is now other software to detwin. One program you can get from S. Ramaswamy (cephalosporin synthase paper). Then there is DETWIN in CCP4. As far as I know, you have to input a twin fraction in DETWIN. You are supposed to find the true value by testing different twin fractions and then checking in TRUNCATE/XLOGGRAPH at which twin fraction your cumulative intensity distribution looks most healthy. Good luck, Roman -- _________________________________________________________________________ Dr. Roman Hillig Institute for Immunogenetics Charite Spandauer Damm 130 D - 14050 Berlin, Germany phone ++49-030-450 53019 e-mail roman.hillig@charite.de fax ++49-030 450 53953 _________________________________________________________________________

**Follow-Ups**:**Re: twinning***From:*"Eleanor J. Dodson" <ccp4@ysbl.york.ac.uk>

**References**:**twinning***From:*Titia Sixma <sixma@nki.nl>

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