Computational Plant Biochemistry

Summary: We present a method for automatic test case generation for protein–protein docking. A consensus-type approach is proposed processing the whole PDB and classifying protein structures into complexes and unbound proteins by combining information from three different approaches (current PDB-at-a-glance classification, search of complexes by sequence identical unbound structures and chain naming). Out of this classification test cases are generated automatically. All calculations were run on the database. The information stored is available via a web interface. The user can choose several criteria for generating his own subset out of our test cases, e.g. for testing docking algorithms.Availability:http://bibiserv.techfak.uni-bielefeld.de/agt-sdp/

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Mass spectrometry is the work-horse technology of the emerging field of metabolomics. Community-wide accepted data models and XML formats for data interchange such as mzData are currently in development. The information contained in these models is sufficient to create applications and databases in a model driven architecture (MDA). This allows to (re-)create the necessary code basis and backend database with minimal manual coding. We present an infrastructure to support the use of these data standards. It uses the Eclipse framework to generate Java objects, XML input/output, database persistence and a user-friendly editor for both the XML files and database content. A prototype of a Web frontend has been created to view, verify and upload to such a repository

For high-throughput screening of genetically modified plant cells, a system for the automatic analysis of huge collections of microscope images is needed to decide whether the cells are infected with fungi or not. To study the potential of feature based classification for this application, we compare different classifiers (kNN, SVM, MLP, LVQ) combined with several feature reduction techniques (PCA, LDA, Mutual Information, Fisher Discriminant Ratio, Recursive Feature Elimination). We achieve a significantly higher classification accuracy using a reduced feature vector instead of the full length feature vector.

We are developing a vendor-independent archive and on top of that a data warehouse for mass spectrometry metabolomics data. The archive schema resembles the communitydeveloped object model, the Java implementation of the model classes, and an editor (for both mzData XML files and the database) have been generated using the Eclipse Modeling Framework. Persistence is handled by the JDO2 -compliant framework JPOX. The main content of the Data Warehouse are the results of the signal processing and peak-picking tasks, carried out using the XCMS package from Bioconductor, putative identification and mass decomposition are added to the warehouse afterwards.We present the system architecture, current content, performance observations and describe the analysis tools on top of the warehouse.Availability: http://msbi.ipb-halle.de/

2D-Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical method to elucidate the chemical structure of molecules. In contrast to 1D-NMR spectra, 2D-NMR spectra correlate the chemical shifts of 1H and 13C simultaneously. To curate or merge large spectra libraries a robust (and fast) duplicate detection is needed. We propose a definition of duplicates with the desired robustness properties mandatory for 2D-NMR experiments. A major gain in runtime performance wrt. previously proposed heuristics is achieved by mapping the spectra to simple discrete objects. We propose several appropriate data transformations for this task. In order to compensate for slight variations of the mapped spectra, we use appropriate hashing functions according to the locality sensitive hashing scheme, and identify duplicates by hash-collisions.

Mass spectrometry is the work-horse technology of the emerging field of metabolomics. The identification of mass signals remains the largest bottleneck for a non-targeted approach: due to the analytical method, each metabolite in a complex mixture will give rise to a number of mass signals. In contrast to GC/MS measurements, for soft ionisation methods such as ESI-MS there are no extensive libraries of reference spectra or established deconvolution methods. We present a set of annotation methods which aim to group together mass signals measured from a single metabolite, based on rules for mass differences and peak shape comparison.Availability: The software and documentation is available as an R package on http://msbi.ipb-halle.de/

Software engeneering today provides tools which minimize the need for manual coding of the typical components of an application, such as database, frontend and web application. Visual modelling brings together users and developers, and allows quick and direct communication about the topic. In the metabolomics community data models and XML formats for data interchange such as mzData are currently emerging. Using these standards as a show case, we present an infrastructure to support the use of these data standards and the process of getting there.

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BackgroundLiquid chromatography coupled to mass spectrometry (LC/MS) is an important analytical technology for e.g. metabolomics experiments. Determining the boundaries, centres and intensities of the two-dimensional signals in the LC/MS raw data is called feature detection. For the subsequent analysis of complex samples such as plant extracts, which may contain hundreds of compounds, corresponding to thousands of features – a reliable feature detection is mandatory.ResultsWe developed a new feature detection algorithm centWave for high-resolution LC/MS data sets, which collects regions of interest (partial mass traces) in the raw-data, and applies continuous wavelet transformation and optionally Gauss-fitting in the chromatographic domain. We evaluated our feature detection algorithm on dilution series and mixtures of seed and leaf extracts, and estimated recall, precision and F-score of seed and leaf specific features in two experiments of different complexity.ConclusionThe new feature detection algorithm meets the requirements of current metabolomics experiments. centWave can detect close-by and partially overlapping features and has the highest overall recall and precision values compared to the other algorithms, matchedFilter (the original algorithm of XCMS) and the centroidPicker from MZmine. The centWave algorithm was integrated into the Bioconductor R-package XCMS and is available from http://www.bioconductor.org/