Can you (or anybody else) expand upon this -- what would be a recommended screening protocol for twinning? Collect X degrees of data, scale, merge, run mmtbx.xtriage? How many degrees of data will it take to give a reliable estimate, and does this depend upon crystal orientation, SG, merohedral vs pseudo-merohedral twinning, other parameters???
We have a pseudo-merohedrally twinned crystal (SG=C2 with beta~90) and the twin fraction was ~0.44 in the two crystals we have tested, but we are now taking 40 new crystals to NSLS and I would welcome advice for how to screen efficiently. Thanks! Evette Evette S. Radisky, Ph.D. Assistant Professor and Associate Consultant II Mayo Clinic Cancer Center Griffin Cancer Research Building, Rm 310 4500 San Pablo Road Jacksonville, FL 32224 (904) 953-6372 (office) (904) 953-2857 (lab) -----Original Message----- From: CCP4 bulletin board [mailto:[EMAIL PROTECTED] On Behalf Of Christopher Colbert Sent: Tuesday, April 17, 2007 4:01 PM To: [email protected] Subject: Re: [ccp4bb] twin fraction varies between crystals? I experienced the same behavior. Crystals from the same drop could have varying twin fractions. Screening for twinning can be done with remarkably few degrees of data. Of course, all proteins and all twins aren't equal. So, don't expect to have varying twin fractions all the time. Happy Refining, Chris On Tue, 17 Apr 2007, Mark Mayer wrote: >>>For cases where people have had merohedral twinning, did the twin >>>fraction vary substantially between individual crystals grown under >>>indentical conditions? I have no prior experience with merohedral >>>twinning, and was surprised to see that the twin fraction varied substantially as detailed below, and that by screening we were able to get untwinned xtals. >>> >>>The project started with a weak home data set for which the twin >>>fraction was 0.478, and which scaled in both H3 and H32. We just came >>>back from APS with data sets from another three crystals, for which >>>the ML twin fraction, estimated using phenix.xtriage with scalepack >>>merged intensities as input, varied from 0.335, 0.219 and 0.02. The latter is refining very nicely, in H3 and will not scale in H32. >>> >>>Thanks - Mark >>> Christopher L. Colbert, Ph.D. Assistant Instructor Phone: (214) 645 5944 University of Texas Southwestern Medical Center FAX: (214) 645 5945 6001 Forest Park Lane Dallas, TX 75390
