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Instruments / Technical Area	Publication Details	Published
	Atomic model validation using the CCP-EM software suite Agnel Praveen Joseph , Mateusz Olek , Sony Malhotra , Peijun Zhang , Kevin Cowtan , Tom Burnley , Martyn Winn Acta Crystallographica Section D Structural Biology 78 DOI: 10.1107/S205979832101278X Open Access Show Abstract ▼ Abstract: Recently, there has been a dramatic improvement in the quality and quantity of data derived using cryogenic electron microscopy (cryo-EM). This is also associated with a large increase in the number of atomic models built. Although the best resolutions that are achievable are improving, often the local resolution is variable, and a significant majority of data are still resolved at resolutions worse than 3 Å. Model building and refinement is often challenging at these resolutions, and hence atomic model validation becomes even more crucial to identify less reliable regions of the model. Here, a graphical user interface for atomic model validation, implemented in the CCP-EM software suite, is presented. It is aimed to develop this into a platform where users can access multiple complementary validation metrics that work across a range of resolutions and obtain a summary of evaluations. Based on the validation estimates from atomic models associated with cryo-EM structures from SARS-CoV-2, it was observed that models typically favor adopting the most common conformations over fitting the observations when compared with the model agreement with data. At low resolutions, the stereochemical quality may be favored over data fit, but care should be taken to ensure that the model agrees with the data in terms of resolvable features. It is demonstrated that further re-refinement can lead to improvement of the agreement with data without the loss of geometric quality. This also highlights the need for improved resolution-dependent weight optimization in model refinement and an effective test for overfitting that would help to guide the refinement process.	Feb 2022
	CCP4i2: the new graphical user interface to the CCP4 program suite Liz Potterton , Jon Agirre , Charles Ballard , Kevin Cowtan , Eleanor Dodson , Phil R. Evans , Huw T. Jenkins , Ronan Keegan , Eugene Krissinel , Kyle Stevenson , Andrey Lebedev , Stuart J. Mcnicholas , Robert A. Nicholls , Martin Noble , Navraj S. Pannu , Christian Roth , George Sheldrick , Pavol Skubak , Johan Turkenburg , Ville Uski , Frank Von Delft , David Waterman , Keith Wilson , Martyn Winn , Marcin Wojdyr Acta Crystallographica Section D Structural Biology 74, 68 - 84 DOI: 10.1107/S2059798317016035 Open Access Show Abstract ▼ Abstract: The CCP4 (Collaborative Computational Project, Number 4) software suite for macromolecular structure determination by X-ray crystallography groups brings together many programs and libraries that, by means of well established conventions, interoperate effectively without adhering to strict design guidelines. Because of this inherent flexibility, users are often presented with diverse, even divergent, choices for solving every type of problem. Recently, CCP4 introduced CCP4i2, a modern graphical interface designed to help structural biologists to navigate the process of structure determination, with an emphasis on pipelining and the streamlined presentation of results. In addition, CCP4i2 provides a framework for writing structure-solution scripts that can be built up incrementally to create increasingly automatic procedures.	Feb 2018
Krios I-Titan Krios I at Diamond	Refinement of atomic models in high resolution EM reconstructions using Flex-EM and local assessment Agnel Praveen Joseph , Sony Malhotra , Tom Burnley , Chris Wood , Daniel K. Clare , Martyn Winn , Maya Topf Methods DOI: 10.1016/j.ymeth.2016.03.007 Open Access Show Abstract ▼ Abstract: As the resolutions of Three Dimensional Electron Microscopic reconstructions of biological macromolecules are being improved, there is a need for better fitting and refinement methods at high resolutions and robust approaches for model assessment. Flex-EM/MODELLER has been used for flexible fitting of atomic models in intermediate-to-low resolution density maps of different biological systems. Here, we demonstrate the suitability of the method to successfully refine structures at higher resolutions (2.5-4.5 Å) using both simulated and experimental data, including a newly processed map of Apo-GroEL. A hierarchical refinement protocol was adopted where the rigid body definitions are relaxed and atom displacement steps are reduced progressively at successive stages of refinement. For the assessment of local fit, we used the SMOC (segment-based Manders’ overlap coefficient) score, while the model quality was checked using the Qmean score. Comparison of SMOC profiles at different stages of refinement helped in detecting regions that are poorly fitted. We also show how initial model errors can have significant impact on the goodness-of-fit. Finally, we discuss the implementation of Flex-EM in the CCP-EM software suite.	Mar 2016
	Evaluating the solution from MrBUMP and BALBES Ronan Keegan , Fei Long , Vincent J. Fazio , Martyn Winn , Garib N. Murshudov , Alexei A. Vagin Acta Crystallographica Section D Biological Crystallography 67 (4), 313 - 323 DOI: 10.1107/S0907444911007530 Open Access Show Abstract ▼ Abstract: Molecular replacement is one of the key methods used to solve the problem of determining the phases of structure factors in protein structure solution from X-ray image diffraction data. Its success rate has been steadily improving with the development of improved software methods and the increasing number of structures available in the PDB for use as search models. Despite this, in cases where there is low sequence identity between the target-structure sequence and that of its set of possible homologues it can be a difficult and time-consuming chore to isolate and prepare the best search model for molecular replacement. MrBUMP and BALBES are two recent developments from CCP4 that have been designed to automate and speed up the process of determining and preparing the best search models and putting them through molecular replacement. Their intention is to provide the user with a broad set of results using many search models and to highlight the best of these for further processing. An overview of both programs is presented along with a description of how best to use them, citing case studies and the results of large-scale testing of the software.	Apr 2011

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