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CCTBX questions
by Morten Grøftehauge 21 Jul '14

21 Jul '14

Hi people, I notice that cctbx.python comes with phenix but as far as I can tell from when I run it, look at imported modules with dir(), and compare to the documentation on Sourceforge the version that comes with phenix is abridged. And possibly not the same version as the sourceforge one but they probably are the same. Will it cause any problems with Phenix if I install cctbx from sourceforge? Is it unnecessary? Second question: Is there any better documentation anywhere? I found James Stroud's wiki but that's mainly for structure factor manipulation. Cheers, Morten -- Morten K Grøftehauge, PhD Pohl Group Durham University

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Long Distant Restraints
by Bradley Hintze 18 Jul '14

18 Jul '14

Hey PHENIX, I am wondering if I can define a distant restraint longer that 3A in a custom restraint file? The conventional way of doing this is to provide : refinement.geometry_restraints.edits { C8_C1=chain C and resid 8 and name C1' D10_C1=chain D and resid 10 and name C1' bond { action = *add atom_selection_1 = $C8_C1 atom_selection_2 = $D10_C1 distance_ideal = 9.1 sigma = 0.02 slack = 0.5 } Obviously this is a distant and not bond restraint. 9.1 exceeds the allowed length of 3 for a bond. Is there a different type of restraint that allows longer distances? Thanks! -- Bradley J. Hintze Duke University PhD Candidate Department of Biochemistry

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Refinement cycles
by George Devaniranjan 17 Jul '14

17 Jul '14

Hi, I was wondering if there is a reason for setting the default number of refinement cycles to 3 in Phenix refine? is there a number of cycles at which point it becomes unacceptable to run so many ? Thank you, George

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B factors too high for low resolution data refinement
by 李翔 15 Jul '14

15 Jul '14

Hi everyone, I am working on my low-resolution data (~6.5 A). When I was doing refinement with PHENIX, the B factors remain pretty high (~400, not sure whether it is normal for the data with such resolution.) And B factors further increased after group B factor refinement (~500). Does it mean the group B factors refinement not working or is there a way I can somehow define a limit for B-factors? (I read one previous topic a few years ago which indicates the B factor can not be controlled. Not sure whether it is available now). Thank you very much for your help! Sincerely, Xiang -- Li Xiang Department of chemistry, Purdue University Email：lixiang1642(a)gmail.com

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So what is unique?
by Kenneth A. Satyshur 15 Jul '14

15 Jul '14

There is some disagreement on terms used to deposit data. We need a definition and an algorithm for each definition. "Unique Reflections" My definition is all the possible reflections out to the highest resolution reported not related by symmetry. Where can I find this? The .mtz contains a list of all HKL calculated to the highest resolution. Usually, we are not able to measure all these diffraction spots due to limits of the detector, mechanical limits, crystal orientation, etc. 'Total reflections' The depositions server asks for total reflections. I assume it wants only those unique reflections we were able to collect, regardless of the sigma cut off. These are called 'observed'. The total we use in refinement will be a subset of the 'unique observed' that are cut on sigma. However, some crystallographers believe that we should not cut on sigma since some of the intensities may in fact be zero. Is this a question for the Refmac and Phenix people? Please give us some guidance and maybe a reference or two that we can use. thanks -- Kenneth A. Satyshur, M.S.,Ph.D. Senior Scientist University of Wisconsin Madison, Wisconsin 53706 608-215-5207

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cifs still in pdb v2
by Guenter Fritz 14 Jul '14

14 Jul '14

Dear Pavel and Nat, can you include in future phenix versions the FAD.cif, NAD.cif and data_NAI.cif / NAI.cif in pdb v3? Currently both are still pdb v2. I usually simply copy the cifs pdb v3 into the mon_lib directory , but sometimes I forget it and stumble over it. Thanks and best wishes, Guenter

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Maximum-likelihood score calculation
by Jouko Virtanen 12 Jul '14

12 Jul '14

Hi all, I would like to calculate the maximum-likelihood score given an input structure and an mtz file. How can I do that? Thanks in advance. Best regards, Jouko

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Real space implementation of DEN refinement?
by Oliver Clarke 11 Jul '14

11 Jul '14

Hi all, Just wondering whether there is any capacity to include DEN restraints in phenix.real_space_refine, e.g. as implemented in the program DireX (see ref below), or any possibility of implementing such in a future release of PHENIX? This would be very handy for refinement of models into low resolution maps (particularly EM maps). Also, on a different but related topic, does anyone have any suggestions as to how to handle model validation (local and global) at low resolution in real-space? It seems as though there is not a solid consensus on how to handle this. Many thanks, Oliver. 1. Schröder, G. F., Brünger, A. T. & Levitt, M. Combining Efficient Conformational Sampling with a Deformable Elastic Network Model Facilitates Structure Refinement at Low Resolution. Structure 15, 1630–1641 (2007).)

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Twinning in data reduction and phenix.refine
by Chen Zhao 11 Jul '14

11 Jul '14

Dear all, I am now dealing with a pseudo-merohedral twin (3.2 A, P1 twinned into C2), and I have a couple of questions concerning the data reduction and refinement: 1) R-free flag in refinement a) For twin refinement, I know the reflections related by the twin law should have the same R-free flag. If I process my data in P1, and generate the R-free flag by phenix.refine using the key word xray_data.r_free_flags.use_lattice_symmetry=True, can phenix generate the R-free flags considering the 2-fold point group symmetry and deal with the twinning properly? b) I read that the R-factor could go down to around 40% in twin refinement in the presence of twinning even if the model is completely wrong. For my understanding, this could be due to the fact that the reflections are correlated by the twin law. If the R-free flags are chosen in the highest lattice symmetry, will the R-free still suffer from this problem? 2) Twin fraction In phenix.xtriage, the predicted twin fraction is about 30%. However, in phenix.refine, the twin_fraction is always between 46% to 50%. Why could this happen? 3) Data reduction I am not very clear about this point, since I just started dealing twinning. But what I am thinking is whether it is a good idea to merge the Friedel pair in the presence of twinning. Since the two twin domains have different hkl index if considering one as the reference, is the Friedel law still valid? This might be a very simple mathematical problem. I really appreciate your answers! Sincerely, Chen

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Anomalous or not?
by CPMAS Chen 10 Jul '14

10 Jul '14

Hi, Phenix Users, I recently collected data at SSRL. I used autoxds and multiscale to merge couple of datasets and hoped to see some anomalous signals. Now comes the questions. 1. if I use the default sigma(=2), then autoxds will report weak anomalous signals and leave the friedel flag off. If I lower sigma to 1.5, it will report strong anomalous signals. 2. when I used Xtriage under Phenix to check the data quality, it reported weak anomalous signal or at above 10A. 3. I used aimless (in CCP4) to merge data, it also reported weak anomalous signal. Which result should I trust? By the way, how can I view/display the ***.anamplot file, which is apparently xmgr format file, but I can not display in CCP4i. Thanks! -- *************************************************** Charles Chen Research Associate University of Pittsburgh School of Medicine Department of Anesthesiology ******************************************************

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