Advances in Xmipp for cryo-electron microscopy: from Xmipp to Scipion

Xmipp is an open-source software package consisting of multiple programs for processing data originating from electron microscopy and electron tomography, designed and managed by the Biocomputing Unit of the Spanish National Center for Biotechnology, although with contributions from many other developers over the world. During its 25 years of existence, Xmipp underwent multiple changes and updates. While there were many publications related to new programs and functionality added to Xmipp, there is no single publication on the Xmipp as a package since 2013. In this article, we give an overview of the changes and new work since 2013, describe technologies and techniques used during the development, and take a peek at the future of the package

Développement de méthodes d'analyse d'images pour les études in vitro et in situ de la variabilité conformationnelle des complexes biomoléculaires par cryo-tomographie électronique : cas d'études de la structure et de la dynamique des nucléosomes

Cryogenic electron tomography (cryo-ET) allows visualizing biomolecular complexes in situ. 3D data of biomolecules produced using cryo-ET are noisy, suffer from spacial anisotropies, and are difficult to analyze individually. Biomolecules are flexible, and analyzing their conformational variability is necessary to understand their functional mechanisms. Standard cryo-ET data processing methods average multiple copies of individual biomolecules to obtain structures at higher resolutions and consider that biomolecular conformational variability is discrete rather than continuous using the classification. This thesis presents the first two cryo-ET data processing methods for analyzing biomolecular continuous conformational variability, HEMNMA-3D and TomoFlow. HEMNMA-3D analyzes experimental data with the motion directions simulated by Normal Mode Analysis and allows the discovery of a large range of biomolecular motions. TomoFlow extracts motions from the data using the computer vision technique of Optical Flow. I show the potential of these two methods on experimental cryo-ET data of nucleosome conformational variability in cells. The two methods show coherent results, shedding light on the conformational variability of nucleosomes in cells.La tomographie électronique cryogénique (cryo-TE) permet de visualiser des complexes biomoléculaires in situ. Les données 3D de biomolécules produites à l'aide de cryo-ET sont bruitées, souffrent d'anisotropies spatiales et sont difficiles à analyser individuellement. Les biomolécules sont flexibles et l'analyse de leur variabilité conformationnelle est nécessaire pour comprendre leurs mécanismes fonctionnels. Les méthodes standards de traitement de données de cryo-ET moyennent plusieurs copies de biomolécules individuelles pour obtenir des structures à des résolutions plus élevées et considèrent que la variabilité conformationnelle biomoléculaire est discrète plutôt que continue en utilisant la classification. Cette thèse présente les deux premières méthodes de traitement de données cryo-ET pour l'analyse de la variabilité conformationnelle continue biomoléculaire, HEMNMA-3D et TomoFlow. HEMNMA-3D analyse des données expérimentales avec les directions de mouvement simulées par l'Analyse de Modes Normaux et permet la découverte d'une large gamme de mouvements biomoléculaires. TomoFlow extrait des mouvements à partir des données en utilisant la technique de vision par ordinateur de Flux Optique. Je montre le potentiel de ces deux méthodes sur des données cryo-ET expérimentales de variabilité conformationnelle des nucléosomes dans les cellules. Les deux méthodes montrent des résultats cohérents, faisant la lumière sur la variabilité conformationnelle des nucléosomes dans les cellules

Développement de méthodes d'analyse d'images pour les études in vitro et in situ de la variabilité conformationnelle des complexes biomoléculaires par cryo-tomographie électronique : cas d'études de la structure et de la dynamique des nucléosomes

La tomographie électronique cryogénique (cryo-TE) permet de visualiser des complexes biomoléculaires in situ. Les données 3D de biomolécules produites à l'aide de cryo-ET sont bruitées, souffrent d'anisotropies spatiales et sont difficiles à analyser individuellement. Les biomolécules sont flexibles et l'analyse de leur variabilité conformationnelle est nécessaire pour comprendre leurs mécanismes fonctionnels. Les méthodes standards de traitement de données de cryo-ET moyennent plusieurs copies de biomolécules individuelles pour obtenir des structures à des résolutions plus élevées et considèrent que la variabilité conformationnelle biomoléculaire est discrète plutôt que continue en utilisant la classification. Cette thèse présente les deux premières méthodes de traitement de données cryo-ET pour l'analyse de la variabilité conformationnelle continue biomoléculaire, HEMNMA-3D et TomoFlow. HEMNMA-3D analyse des données expérimentales avec les directions de mouvement simulées par l'Analyse de Modes Normaux et permet la découverte d'une large gamme de mouvements biomoléculaires. TomoFlow extrait des mouvements à partir des données en utilisant la technique de vision par ordinateur de Flux Optique. Je montre le potentiel de ces deux méthodes sur des données cryo-ET expérimentales de variabilité conformationnelle des nucléosomes dans les cellules. Les deux méthodes montrent des résultats cohérents, faisant la lumière sur la variabilité conformationnelle des nucléosomes dans les cellules.Cryogenic electron tomography (cryo-ET) allows visualizing biomolecular complexes in situ. 3D data of biomolecules produced using cryo-ET are noisy, suffer from spacial anisotropies, and are difficult to analyze individually. Biomolecules are flexible, and analyzing their conformational variability is necessary to understand their functional mechanisms. Standard cryo-ET data processing methods average multiple copies of individual biomolecules to obtain structures at higher resolutions and consider that biomolecular conformational variability is discrete rather than continuous using the classification. This thesis presents the first two cryo-ET data processing methods for analyzing biomolecular continuous conformational variability, HEMNMA-3D and TomoFlow. HEMNMA-3D analyzes experimental data with the motion directions simulated by Normal Mode Analysis and allows the discovery of a large range of biomolecular motions. TomoFlow extracts motions from the data using the computer vision technique of Optical Flow. I show the potential of these two methods on experimental cryo-ET data of nucleosome conformational variability in cells. The two methods show coherent results, shedding light on the conformational variability of nucleosomes in cells

Développement de méthodes d'analyse d'images pour les études in vitro et in situ de la variabilité conformationnelle des complexes biomoléculaires par cryo-tomographie électronique : cas d'études de la structure et de la dynamique des nucléosomes

Cryogenic electron tomography (cryo-ET) allows visualizing biomolecular complexes in situ. 3D data of biomolecules produced using cryo-ET are noisy, suffer from spacial anisotropies, and are difficult to analyze individually. Biomolecules are flexible, and analyzing their conformational variability is necessary to understand their functional mechanisms. Standard cryo-ET data processing methods average multiple copies of individual biomolecules to obtain structures at higher resolutions and consider that biomolecular conformational variability is discrete rather than continuous using the classification. This thesis presents the first two cryo-ET data processing methods for analyzing biomolecular continuous conformational variability, HEMNMA-3D and TomoFlow. HEMNMA-3D analyzes experimental data with the motion directions simulated by Normal Mode Analysis and allows the discovery of a large range of biomolecular motions. TomoFlow extracts motions from the data using the computer vision technique of Optical Flow. I show the potential of these two methods on experimental cryo-ET data of nucleosome conformational variability in cells. The two methods show coherent results, shedding light on the conformational variability of nucleosomes in cells.La tomographie électronique cryogénique (cryo-TE) permet de visualiser des complexes biomoléculaires in situ. Les données 3D de biomolécules produites à l'aide de cryo-ET sont bruitées, souffrent d'anisotropies spatiales et sont difficiles à analyser individuellement. Les biomolécules sont flexibles et l'analyse de leur variabilité conformationnelle est nécessaire pour comprendre leurs mécanismes fonctionnels. Les méthodes standards de traitement de données de cryo-ET moyennent plusieurs copies de biomolécules individuelles pour obtenir des structures à des résolutions plus élevées et considèrent que la variabilité conformationnelle biomoléculaire est discrète plutôt que continue en utilisant la classification. Cette thèse présente les deux premières méthodes de traitement de données cryo-ET pour l'analyse de la variabilité conformationnelle continue biomoléculaire, HEMNMA-3D et TomoFlow. HEMNMA-3D analyse des données expérimentales avec les directions de mouvement simulées par l'Analyse de Modes Normaux et permet la découverte d'une large gamme de mouvements biomoléculaires. TomoFlow extrait des mouvements à partir des données en utilisant la technique de vision par ordinateur de Flux Optique. Je montre le potentiel de ces deux méthodes sur des données cryo-ET expérimentales de variabilité conformationnelle des nucléosomes dans les cellules. Les deux méthodes montrent des résultats cohérents, faisant la lumière sur la variabilité conformationnelle des nucléosomes dans les cellules

Methods for analyzing continuous conformational variability of biomolecules in cryo electron subtomograms: HEMNMA-3D vs. traditional classification

Cryogenic electron tomography (cryo-ET) allows studying biological macromolecular complexes in cells by threedimensional (3D) data analysis. The complexes continuously change their shapes (conformations) to achieve biological functions. The shape heterogeneity in the samples imaged in the cryo electron microscope is a bottleneck for comprehending biological mechanisms and developing drugs. Low signal-to-noise ratio and spatial anisotropy (missing wedge artefacts) make cryo-ET data particularly challenging for resolving the shape variability. Other shape variability analysis techniques simplify the problem by considering discrete rather than continuous conformational changes of complexes. Recently, HEMNMA-3D was introduced for cryo-ET continuous shape variability analysis, based on elastic and rigid-body 3D registration between simulated shapes and cryo-ET data. The simulated motions are obtained by normal mode analysis of a high-or lowresolution 3D reference model of the complex under study. The rigid-body alignment is achieved via fast rotational matching with missing wedge compensation. HEMNMA-3D provides a visual insight into molecular dynamics by grouping and averaging subtomograms of similar shapes and by animating movies of registered motions. This article reviews the method and compares it with existing literature on a simulated dataset for nucleosome shape variability

Comparison between HEMNMA-3D and Traditional Classification Techniques for Analyzing Biomolecular Continuous Shape Variability in Cryo Electron Subtomograms

International audienceCryogenic electron tomography (cryo-ET) allows studying biological macromolecular complexes in cells by threedimensional (3D) data analysis. The complexes continuously change their shapes (conformations) to achieve biological functions. The shape heterogeneity in cryo-ET is a bottleneck for comprehending biological mechanisms and developing drugs. Cryo-ET data suffer from a low signal-to-noise ratio and spatial anisotropies (missing wedge artefacts), making it particularly challenging for resolving the shape variability. Other shape variability analysis techniques simplify the problem by considering discrete rather than continuous conformational changes of complexes. Recently, HEMNMA-3D was introduced for cryo-ET continuous shape variability analysis, based on elastic and rigid-body 3D registration between simulated shapes and cryo-ET data using normal mode analysis and fast rotational matching with missing wedge compensation. HEMNMA-3D provides a visual insight into molecular dynamics by grouping and averaging subtomograms of similar shapes and by animating movies of registered motions. This article reviews HEMNMA-3D and compares it with existing literature on a simulated dataset for nucleosome shape variability

Code and test data of ContinuousFlex plugin for analyzing continuous conformational variability of biomolecular complexes in cryo-EM and cryo-ET data

ContinuousFlex allows analyzing single particle cryo electron microscopy data and in vitro and in situ cryo electron subtomogram data for continuous conformational variability of biomolecular complexes. It has been developed as a plugin of Scipion 3 software (https://github.com/scipion-em/scipion-em-continuousflex). Currently, ContinuousFlex provides HEMNMA, StructMap, HEMNMA-3D and TomoFlow methods. -HEMNMA: Hybrid Electron Microscopy Normal Mode Analysis method to interpret heterogeneity of a set of single particle cryo-EM images in terms of continuous macromolecular conformational transitions [1-3] -StructMap: Structural Mapping method to interpret heterogeneity of a set of single particle cryo-EM maps in terms of continuous conformational transitions [4] -HEMNMA-3D: Extension of HEMNMA to continuous conformational variability analysis of macromolecules from in situ cryo-ET subtomograms [5,7] -TomoFlow: Method for analyzing continuous conformational variability of macromolecules in in vitro and in situ cryogenic subtomograms based on 3D dense optical flow [8-9]Notes: -The plugin additionally provides the test data and automated tests of the protocols in Scipion 3. The following two types of tests of HEMNMA and HEMNMA-3D can be produced by running, in the terminal, "scipion3 tests continuousflex.tests.test_workflow_HEMNMA" and “scipion3 tests continuousflex.tests.test_workflow_HEMNMA3D”, respectively: (1) tests of the entire protocol with the flexible references coming from an atomic structure and from an EM map; and (2) test of the alignment module (test run using 5 MPI threads). The automated tests of the TomoFlow method are also available and can be run using "scipion3 tests continuousflex.tests.test_workflow_TomoFlow". -HEMNMA additionally provides tools for synthesizing noisy and CTF-affected single particle cryo-EM images with flexible or rigid biomolecular conformations, for several types of conformational distributions, from a given atomic structure or an EM map. One part of the noise is applied on the ideal projections before and the other after the CTF, as described in [6]. -HEMNMA-3D additionally provides tools for synthesizing noisy, CTF and missing wedge affected cryo-ET tomograms and single particle subtomograms with flexible or rigid biomolecular conformations, for several types of conformational distributions, from a given atomic structure or an EM map. One part of the noise is applied on the ideal projections before and the other after the CTF, as described in [6]. -A reproduction of some utility codes with their corresponding licenses are contained in this plugin for subtomogram averaging, missing wedge correction, denoising and data reading. These codes are not used in the methods above, but they are made optional for data preprocessing and visualization.References:[1] Jin Q, Sorzano CO, de la Rosa-Trevin JM, Bilbao-Castro JR, Nunez-Ramirez R, Llorca O, Tama F, Jonic S: Iterative elastic 3D-to-2D alignment method using normal modes for studying structural dynamics of large macromolecular complexes. Structure 2014, 22:496-506.[2] Jonic S: Computational methods for analyzing conformational variability of macromolecular complexes from cryo-electron microscopy images. Curr Opin Struct Biol 2017, 43:114-121.[3] Harastani M, Sorzano CO, Jonic S: Hybrid Electron Microscopy Normal Mode Analysis with Scipion. Protein Sci 2020, 29:223-36.[4] Sanchez Sorzano CO, Alvarez-Cabrera AL, Kazemi M, Carazo JM, Jonic S: StructMap: Elastic Distance Analysis of Electron Microscopy Maps for Studying Conformational Changes. Biophys J 2016, 110:1753-1765.[5] Harastani M, Eltsov M, Leforestier A, Jonic S: HEMNMA-3D: Cryo Electron Tomography Method Based on Normal Mode Analysis to Study Continuous Conformational Variability of Macromolecular Complexes. Front Mol Biosci 2021, 8:663121.[6] Jonic S, Sorzano CO, Thevenaz P, El-Bez C, De Carlo S, Unser M: Spline-based image-to-volume registration for three-dimensional electron microscopy. Ultramicroscopy 2005, 103:303-317. [7] Harastani M and Jonic S: Methods for analyzing continuous conformational variability of biomolecules in cryo electron subtomograms: HEMNMA-3D vs. traditional classification. BioRxiv 2021 (https://doi.org/10.1101/2021.10.14.464366)[8] Harastani M, Eltsov M, Leforestier A, Jonic S: TomoFlow: Analysis of continuous conformational variability of macromolecules in cryogenic subtomograms based on 3D dense optical flow. J Mol Biol 2021, 167381.[9] Harastani M and Jonic S: Synthetic cryo electron subtomograms containing biomolecular complexes with continuous conformational variability.[Data set] Zenodo. 2021 (https://doi.org/10.5281/zenodo.5718820)

HEMNMA-3D: Cryo Electron Tomography Method Based on Normal Mode Analysis to Study Continuous Conformational Variability of Macromolecular Complexes

International audienceCryogenic electron tomography (cryo-ET) allows structural determination of biomolecules in their native environment (\textit{in situ}). Its potential of providing information on the dynamics of macromolecular complexes in cells is still largely unexploited, due to the challenges of the data analysis. The crowded cell environment and continuous conformational changes of complexes make difficult disentangling the data heterogeneity. We present HEMNMA-3D, which is, to the best of our knowledge, the first method for analyzing cryo electron subtomograms in terms of continuous conformational changes of complexes. HEMNMA-3D uses a combination of elastic and rigid-body 3D-to-3D iterative alignments of a flexible 3D reference (atomic structure or electron microscopy density map) to match the conformation, orientation, and position of the complex in each subtomogram. The elastic matching combines molecular mechanics simulation (Normal Mode Analysis of the 3D reference) and experimental, subtomogram data analysis. The rigid-body alignment includes compensation for the missing wedge, due to the limited tilt angle of cryo-ET. The conformational parameters (amplitudes of normal modes) of the complexes in subtomograms obtained through the alignment are processed to visualize the distribution of conformations in a space of lower dimension (typically, 2D or 3D) referred to as space of conformations. This allows a visually interpretable insight into the dynamics of the complexes, by calculating 3D averages of subtomograms with similar conformations from selected (densest) regions and by recording movies of the 3D reference's displacement along selected trajectories through the densest regions. We describe HEMNMA-3D and show its validation using synthetic datasets. We apply HEMNMA-3D to an experimental dataset describing \textit{in situ} nucleosome conformational variability. HEMNMA-3D software is available freely (open-source) as part of ContinuousFlex plugin of Scipion V3.0 (http://scipion.i2pc.es)

MDSPACE and MDTOMO Software for Extracting Continuous Conformational Landscapes from Datasets of Single Particle Images and Subtomograms Based on Molecular Dynamics Simulations: Latest Developments in ContinuousFlex Software Package

International audienceCryo electron microscopy (cryo-EM) instrumentation allows obtaining 3D reconstruction of the structure of biomolecular complexes in vitro (purified complexes studied by single particle analysis) and in situ (complexes studied in cells by cryo electron tomography). Standard cryo-EM approaches allow high-resolution reconstruction of only a few conformational states of a molecular complex, as they rely on data classification into a given number of classes to increase the resolution of the reconstruction from the most populated classes while discarding all other classes. Such discrete classification approaches result in a partial picture of the full conformational variability of the complex, due to continuous conformational transitions with many, uncountable intermediate states. In this article, we present the software with a user-friendly graphical interface for running two recently introduced methods, namely, MDSPACE and MDTOMO, to obtain continuous conformational landscapes of biomolecules by analyzing in vitro and in situ cryo-EM data (single particle images and subtomograms) based on molecular dynamics simulations of an available atomic model of one of the conformations. The MDSPACE and MDTOMO software is part of the open-source ContinuousFlex software package (starting from version 3.4.2 of ContinuousFlex), which can be run as a plugin of the Scipion software package (version 3.1 and later), broadly used in the cryo-EM field

TomoFlow: Analysis of continuous conformational variability of macromolecules in cryogenic subtomograms based on 3D dense optical flow

International audienceCryogenic Electron Tomography (cryo-ET) allows structural and dynamics studies of macromolecules in situ. Averaging different copies of imaged macromolecules is commonly used to obtain their structure at higher resolution and discrete classification to analyze their dynamics. Instrumental and data processing developments are progressively equipping cryo-ET studies with the ability to escape the trap of classification into a complete continuous conformational variability analysis. In this work, we propose TomoFlow, a method for analyzing macromolecular continuous conformational variability in cryo-ET subtomograms based on a three-dimensional dense optical flow (OF) approach. The resultant lower-dimensional conformational space allows generating movies of macromolecular motion and obtaining subtomogram averages by grouping conformationally similar subtomograms. The animations and the subtomogram group averages reveal accurate trajectories of macromolecular motion based on a novel mathematical model that makes use of OF properties. This paper describes TomoFlow with tests on simulated datasets generated using different techniques, namely Normal Mode Analysis and Molecular Dynamics Simulation. It also shows an application of TomoFlow on a dataset of nucleosomes in situ, which provided promising results coherent with previous findings using the same dataset but without imposing any prior knowledge on the analysis of the conformational variability. The method is discussed with its potential uses and limitations