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Twin Refinement in P 1 21 1
by Yuri 26 Sep '11

26 Sep '11

Hello everyone, I have a twinned data set with PM twin operator h,-k,-h-l I was able to input the twin law into the refinement parameters, however I do not see a place that asks me for the law when generating the Rfree flags. Could someone point me in the right direction? Best, -- Yuri Pompeu

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renaming an holo PDB after the alo one
by Francois Berenger 26 Sep '11

26 Sep '11

Hello, I have one bound complexe (a ligand + a protein in holo conformation). I also have the apo structure for a very similar protein. Is there a tool to create a new PDB, whose coordinates are taken from the holo structure but residue names and numbers are taken from the alo structure (by looking at the corresponding residues in the output of a sequence alignment program)? I thought about doing a script using clustalw for the alignment part, but the task seems not trivial. Thanks a lot, Francois.

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real space residuals
by Bradley Hintze 26 Sep '11

26 Sep '11

Hey phenix, I see a util for real space correlation. Real space residuals are slightly different. Is the a tool to calculate RSR in phenix? -- Bradley J. Hintze Duke University Graduate Student Department of Biochemistry

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map CC given a model and map coefficients
by Francis E Reyes 26 Sep '11

26 Sep '11

Hi all I'd like to compute a resid by resid and overall map CC between a set of coefficients I specify and a model. Any utils to get this to me quickly? phenix.model_vs_data doesn't seem to take in custom coefficients. Thanks! F --------------------------------------------- Francis E. Reyes M.Sc. 215 UCB University of Colorado at Boulder

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Pseudo-merohedral twinning refinement in C2, when beta = 94 degrees
by John Pak 21 Sep '11

21 Sep '11

Hi all, I currently have a dataset that scales well in C2. (a = 224,b = 129,c = 392. beta= 94.5 degrees). Previously, I had thought that these crystals were in P6322 (posted this a few months ago), but I've since grown better crystals, where the beta angle is now 94.5, and not close to 90.0. I'm reasonably confident with the scaling - however, it has always been really difficult to index these crystals in HKL2000. Like the previous crystals, this new C2 dataset looks like it might be perfectly twinned, based on Xtriage's L test. I've solved the structure by MR, and refined it to 3.0 angstroms to R=30%, Rfree=33%, but I am running out of things to fix. I'd like to perform twinning refinement, based on this Xtriage L test result. The problem is that Xtriage cannot find any pseudomerohedral twinning laws, likely because the beta angle is too far from 90 degrees?? For kicks and giggles, I started to enter arbitrary beta angles in Xtriage, and at a beta angle below 93.4, Xtriage can find two twinning laws (closer to 90 degrees, Xtriage can find 5 twin laws). Using "-1/2*h+3/2*k, 1/2*h+1/2*k, -l" in Phenix refine (the beta angle is still 94.5 degrees, I haven't changed this) results in the R and Rfree dropping a lot to 25.5 and 28.6, respectively. Used the same random seed as previous runs to generate the test set from the scalepack file, with the "use lattice symmetry to generate test set" flag enabled. The maps look a lot noisier. So my questions are: 1. Is this twinning refinement valid? I'm really thinking no - since the maps didn't improve. Suppose the maps didn't get worse though - would this twinning refinement then be valid? 2. How do I go about reindexing this dataset in I2? i.e. to see if the beta angle with this unit cell selection is closer to 90 degrees. Would this even help, with respect to pseudomerohedral twinning refinement? Thanks!

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Maps Bias
by Yuri 21 Sep '11

21 Sep '11

I was having a discussion with a friend about maps and model bias. Is the Fobs/PHImodel more biased than 2FOFCWT/PHI2FOFCWt? What about an omit region of these two? Thanks for any opinion on this -- Yuri Pompeu

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Ligand / Loop occupancy refinement
by Antony Oliver 19 Sep '11

19 Sep '11

Dear all, Apologies if this has been covered already in a previous post — but I can't find a suitable response in the archive. We have the following situation... We have soaked a ligand into an apo-crystal, collected diffraction data, and solved the structure. What is apparent from the electron density, is that the ligand isn't in the crystal at full occupancy, it's roughly about 70-80%. However, as the ligand binds, it causes a small conformation change in the active site of the protein, altering the position of around 4 amino acids. What I want to do, and can't quite get phenix.refine to do is the following... Refine the occupancy of the ligand (chain C resname LIG) with the "A" conformation of the active site residues (which should be the same, as they are mutually dependent) — and then refine the occupancy of the "B" conformation of the active site residues — which should all theoretically add up to a total of 1. Could anyone help me with how the occupancies / constrained_group parameters should be set up in this case? With thanks, Tony. --- Dr Antony W Oliver Senior Research Fellow CR-UK DNA Repair Enzymes Group Genome Damage and Stability Centre Science Park Road University of Sussex Falmer, Brighton, BN1 9RQ email: antony.oliver(a)sussex.ac.uk<mailto:[email protected]> tel (office): +44 (0)1273 678349 tel (lab): +44 (0)1273 677512

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bulk solvent mask question
by Laurie Betts 16 Sep '11

16 Sep '11

I notice that during refinement of a MR solution for a protein (search model is 100% homologous to target), a very large ligand-binding cavity (as much as 20 A wide in some parts) in my protein gives weak positive difference density for a ligand soaked into the crystals, unless I turn off bulk solvent modeling. Then the fo-fc difference density is quite strong (2.6 Angstrom data). I think this is due to part of the cavity being included in bulk solvent? Can I edit the mask easily, or flag parts of the protein as NOT exposed to solvent? Thanks Laurie Betts

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Refinement with optimize weights
by Ankit Gupta 16 Sep '11

16 Sep '11

Hello Forum, I am using Phenix 1.7.1-743 to refine my structure. My R/Rfree values for a 2.5 A structure were 0.22/0.305. I used optimize weights along with TLS and the R/Rfree values improved to 0.23/0.29. I wanted to know what parameters should I use for subsequent refinement. I read on phenix bb that one needs to fix the wxc_scale and wxu_scale. Is this correct? What values should be used for these parameters after running optimize wxc/wxu weights. Is there any place where I can get starting values for my future refinement? Also, I would like to know what Fix X-ray/stereochemistry weight and Fix X-ray/ADP weights are for? Thanks for the help.

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Phenix.refine distorts geometry during rigid body refinement
by Ian Slaymaker 14 Sep '11

14 Sep '11

I am bringing a PDB refined in Refmac back to phenix.refine. After an initial rigid body refinement to compare numbers (one chain per group), the geometry (specifically the bond length rmsd) had surprisingly increased. Phenix.validate confirmed the Refmac (initial) geometry numbers and then afterwards confirmed the distorted geometry. What is strange is that when opened in COOT, the initial and final models are completely super imposed. REMARK Start: r_work = 0.3375 r_free = 0.3624 bonds = 0.006 angles = 0.768 REMARK Final: r_work = 0.3379 r_free = 0.3626 bonds = 0.145 angles = 1.019 can you help me figure out what is going on here? These are the final few refinements of a 4.1 A structure. Thanks, Ian

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