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1.  Visual automated macromolecular model building 
The molecular viewer ArpNavigator allows easy execution of ARP/wARP model-building routines while model-update steps are shown in real time, rendering the whole process transparent to the user.
Automated model-building software aims at the objective interpretation of crystallographic diffraction data by means of the construction or completion of macromolecular models. Automated methods have rapidly gained in popularity as they are easy to use and generate reproducible and consistent results. However, the process of model building has become increasingly hidden and the user is often left to decide on how to proceed further with little feedback on what has preceded the output of the built model. Here, ArpNavigator, a molecular viewer tightly integrated into the ARP/wARP automated model-building package, is presented that directly controls model building and displays the evolving output in real time in order to make the procedure transparent to the user.
PMCID: PMC3606041  PMID: 23519672
model building; ARP/wARP; molecular graphics
2.  Use of noncrystallographic symmetry for automated model building at medium to low resolution 
Noncrystallographic symmetry is automatically detected and used to achieve higher completeness and greater accuracy of automatically built protein structures at resolutions of 2.3 Å or poorer.
A novel method is presented for the automatic detection of noncrystallographic symmetry (NCS) in macromolecular crystal structure determination which does not require the derivation of molecular masks or the segmentation of density. It was found that throughout structure determination the NCS-related parts may be differently pronounced in the electron density. This often results in the modelling of molecular fragments of variable length and accuracy, especially during automated model-building procedures. These fragments were used to identify NCS relations in order to aid automated model building and refinement. In a number of test cases higher completeness and greater accuracy of the obtained structures were achieved, specifically at a crystallo­graphic resolution of 2.3 Å or poorer. In the best case, the method allowed the building of up to 15% more residues automatically and a tripling of the average length of the built fragments.
PMCID: PMC3322604  PMID: 22505265
noncrystallographic symmetry; automated model building
3.  On the combination of molecular replacement and single-wavelength anomalous diffraction phasing for automated structure determination 
The combination of molecular replacement and single-wavelength anomalous diffraction improves the performance of automated structure determination with Auto-Rickshaw.
A combination of molecular replacement and single-wavelength anomalous diffraction phasing has been incorporated into the automated structure-determination platform Auto-Rickshaw. The complete MRSAD procedure includes molecular replacement, model refinement, experimental phasing, phase improvement and automated model building. The improvement over the standard SAD or MR approaches is illustrated by ten test cases taken from the JCSG diffraction data-set database. Poor MR or SAD phases with phase errors larger than 70° can be improved using the described procedure and a large fraction of the model can be determined in a purely automatic manner from X-ray data extending to better than 2.6 Å resolution.
PMCID: PMC2756167  PMID: 19770506
automated structure determination; molecular replacement; single-wavelength anomalous diffraction
4.  Interpretation of very low resolution X-ray electron-density maps using core objects 
The interpretation of a 20 Å resolution electron-density map using segmentation and pattern-recognition-based identification of domain shapes is described.
A novel approach to obtaining structural information from macromolecular X-ray data extending to resolutions as low as 20 Å is presented. Following a simple map-segmentation procedure, the approximate shapes of the domains forming the structure are identified. A pattern-recognition comparative analysis of these shapes and those derived from the structures of domains from the PDB results in candidate structural models that can be used for a fit into the density map. It is shown that the placed candidate models can be employed for subsequent phase extension to higher resolution.
PMCID: PMC2703575  PMID: 19564689
core objects; low-resolution electron-density maps; map segmentation; pattern recognition
5.  A knowledge-driven approach for crystallographic protein model completion 
A novel method that uses the conformational distribution of Cα atoms in known structures is used to build short missing regions (‘loops’) in protein models. An initial tree of possible loop paths is pruned according to structural and electron-density criteria and the most likely loop conformation(s) are selected and built.
One of the most cumbersome and time-demanding tasks in completing a protein model is building short missing regions or ‘loops’. A method is presented that uses structural and electron-density information to build the most likely conformations of such loops. Using the distribution of angles and dihedral angles in pentapeptides as the driving parameters, a set of possible conformations for the Cα backbone of loops was generated. The most likely candidate is then selected in a hierarchical manner: new and stronger restraints are added while the loop is built. The weight of the electron-density correlation relative to geometrical considerations is gradually increased until the most likely loop is selected on map correlation alone. To conclude, the loop is refined against the electron density in real space. This is started by using structural information to trace a set of models for the Cα backbone of the loop. Only in later steps of the algorithm is the electron-density correlation used as a criterion to select the loop(s). Thus, this method is more robust in low-density regions than an approach using density as a primary criterion. The algorithm is implemented in a loop-building program, Loopy, which can be used either alone or as part of an automatic building cycle. Loopy can build loops of up to 14 residues in length within a couple of minutes. The average root-mean-square deviation of the Cα atoms in the loops built during validation was less than 0.4 Å. When implemented in the context of automated model building in ARP/wARP, Loopy can increase the completeness of the built models.
PMCID: PMC2467521  PMID: 18391408
model building; loop modelling; Loopy
6.  ARP/wARP and molecular replacement: the next generation 
A systematic test shows how ARP/wARP deals with automated model building for structures that have been solved by molecular replacement. A description of protocols in the flex-wARP control system and studies of two specific cases are also presented.
Automatic iterative model (re-)building, as implemented in ARP/wARP and its new control system flex-wARP, is particularly well suited to follow structure solution by molecular replacement. More than 100 molecular-replacement solutions automatically solved by the BALBES software were submitted to three standard protocols in flex-wARP and the results were compared with final models from the PDB. Standard metrics were gathered in a systematic way and enabled the drawing of statistical conclusions on the advantages of each protocol. Based on this analysis, an empirical estimator was proposed that predicts how good the final model produced by flex-wARP is likely to be based on the experimental data and the quality of the molecular-replacement solution. To introduce the differences between the three flex-wARP protocols (keeping the complete search model, converting it to atomic coordinates but ignoring atom identities or using the electron-density map calculated from the molecular-replacement solution), two examples are also discussed in detail, focusing on the evolution of the models during iterative rebuilding. This highlights the diversity of paths that the flex-wARP control system can employ to reach a nearly complete and accurate model while actually starting from the same initial information.
PMCID: PMC2394809  PMID: 18094467
model building; refinement; molecular replacement
7.  Assessment of automatic ligand building in ARP/wARP  
The performance of the ligand-building module of the ARP/wARP software suite is assessed through a large-scale test on known protein–ligand complexes. The results provide a detailed benchmark and guidelines for future improvements.
The efficiency of the ligand-building module of ARP/wARP version 6.1 has been assessed through extensive tests on a large variety of protein–ligand complexes from the PDB, as available from the Uppsala Electron Density Server. Ligand building in ARP/wARP involves two main steps: automatic identification of the location of the ligand and the actual construction of its atomic model. The first step is most successful for large ligands. The second step, ligand construction, is more powerful with X-ray data at high resolution and ligands of small to medium size. Both steps are successful for ligands with low to moderate atomic displacement parameters. The results highlight the strengths and weaknesses of both the method of ligand building and the large-scale validation procedure and help to identify means of further improvement.
PMCID: PMC2483501  PMID: 17164533
ligand binding; ARP/wARP

Results 1-7 (7)