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Paul, We've been able to solve a structure from crystals that have a unit cell very similar to yours. The following measures were critical in reducing spot overlaps along the long cell axis (725 Angstrom in our case): - try to freeze your crystals with the long cell axis along the rotation axis. We also had rod-shaped hexagonal crystals and the long cell axis turned out to be parallel to longest edge of the crystal, which made it relatively easy to freeze the crystals in the right orientation. - reduce the beamsize: a small beam results in smaller reflections and reduces overlaps. If you were collecting at the ID23 microfocus beamline then your beamsize was probably close to optimal. - move away the detector as far as possible from the crystal. Of course, here's a trade-off with resolution. However, with the new 3x3 array detectors at most ESRF beamlines that shouldn't be a problem anymore. You could still move away the detector without sacrificing the high resolution reflections (we were able to resolve the long axis down to 2.8 Angstrom on a 3x3 detector). - focus the beam on the detector rather than on the crystal. (check with the beamline scientist - we were only allowed to tweak this at the PXII beamline at SLS). - if the data still suffer from overlaps, you could increase the wavelength of the beam (unfortunately not possible at ID23-2). As far as data processing is concerned, the newest version of Mosflm (6.2.6) is able to properly index our data with the long cell axis. We were able to solve the structure with data that were processed with HKL2000 prior to the release of the latest version of mosflm. Let me know if it works and good luck. Cheers. -Chris -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Behalf Of Paul McEwan Sent: donderdag 15 juni 2006 16:28 To: [email protected] Subject: [ccp4bb]: difficult crystal diffraction *** For details on how to be removed from this list visit the *** *** CCP4 home page http://www.ccp4.ac.uk *** Dear all, hopefully some of you may be able to make a few suggestions for a project I'm currently working on. It's a protein complex which crystallises to produce small crystals (max. dimension 0.1 mm, with rod morphology). It doesn't diffract in-house but does at synchrotron sources. The data is very anisotropic and a massive unit cell. I believe the indexing is P6 or P622 with cell dimensions 87.8, 87.8, 629.5. I've had a lot of problems scaling any data (I think, mainly due to overlaps or poor data and the anisotropy of diffraction). The crystals are frozen (but I do intend on trying some capillary mounted samples). Any suggestions regarding processing the data or optimising the data collection strategy would be wellcomed. If you would like to look at a typical frame collected at the ESRF on id23 at a distance of 445mm and a wavelength of 1.0 Ang. please feel free to download it from here: http://www.nottingham.ac.uk/~pazxtal Regards, Paul.. ################################## Dr Paul A. McEwan Post-Doctoral Research Fellow Protein Crystallography Group Centre for Biomolecular Science Clifton Boulevard University of Nottingham Nottingham NG7 2RD Tel: 0115 8468009 http://www.nottingham.ac.uk/~pazxtal ################################## This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.
