MOTIVATION: Pairwise alignment of protein structures is a fundamental task in structural bioinformatics. There are numerous computer programs in the public domain that produce alignments for a given pair of protein structures, but the results obtained by the various programs generally differ substantially. Hence, in the application of such programs the question arises which of the alignment programs are the most trustworthy in the sense of overall performance, and which programs provide the best result for a given pair of proteins. The major problem in comparing, evaluating and judging alignment results is that there is no clear notion of the optimality of an alignment. As a consequence, the numeric criteria and scores reported by the individual structure alignment programs are largely incomparable. RESULTS: Here we report on the development and application of a new approach for the evaluation of structure alignment results. The method uses the translation vector and rotation matrix to generate the superposition of two structures but discards the alignment reported by the individual programs. The optimal alignment is then generated in standardized form based on a suitably implemented dynamic programming algorithm where the length of the alignment is the single most informative parameter. We demonstrate that some of the most popular programs in protein structure research differ considerably in their overall performance. In particular, each of the programs investigated here produced in at least in one case the best and the worst alignment compared with all others. Hence, at the current state of development of structure comparison techniques, it is advisable to use several programs in parallel and to choose the optimal alignment in the way reported here. AVAILABILITY AND IMPLEMENTATION: The computer software that implement the method described here is freely available at http://melolab.org/stovca.

SUMMARY: The performance of sequence database search methods is usually judged by receiver operating characteristic (ROC) analysis. The proper interpretation of the results obtained and a fair comparison across different methods critically depends on the properties of the data set used for such an analysis; in particular, each query must have the same number of true positives and true negatives. Here, we present a novel web service based on a dataset specifically designed for ROC analysis and the investigation of alignment quality. The data set is derived from a quantitative classification of protein structures (COPS), while analysis and results are presented through an intuitive web interface. The analysis provides details such as false positives per query, and visualization of the structural similarity between query and targets. Most importantly, results obtained for a specific alignment method are immediately related to those obtained for several popular standard sequence alignment methods.

UNLABELLED: The accuracy of current signal peptide predictors is outstanding. The most successful predictors are based on neural networks and hidden Markov models, reaching a sensitivity of 99% and an accuracy of 95%. Here, we demonstrate that the popular BLASTP alignment tool can be tuned for signal peptide prediction reaching the same high level of prediction success. Alignment-based techniques provide additional benefits. In spite of high success rates signal peptide predictors yield false predictions. Simple sequences like polyvaline, for example, are predicted as signal peptides. The general architecture of learning systems makes it difficult to trace the cause of such problems. This kind of false predictions can be recognized or avoided altogether by using sequence comparison techniques. Based on these results we have implemented a public web service, called Signal-BLAST. Predictions returned by Signal-BLAST are transparent and easy to analyze. AVAILABILITY: Signal-BLAST is available online at http://sigpep.services.came.sbg.ac.at/signalblast.html.

Metric information on similarities and distances in fold space is essential for quantitative work in structural bioinformatics and structural biology. Here we derive a suitable metric for protein structures from the fundamental axioms of similarity. Derivation of the metric also clarifies the relationship between the interrelated concepts of distance and similarity.

UNLABELLED: The database of known protein structures contains an overwhelming number of structural similarities that frequently point to intriguing biological relationships. The similarities are often difficult to spot, and once detected their comprehension needs proper visualization. Here we introduce the new concept of a Fold Space Navigator, a user interface enabling the efficient navigation through fold space and the instantaneous visualization of pairwise structure similarities. AVAILABILITY: The Fold Space Navigator is accessible as a public web service at http://services.came.sbg.ac.at

UNLABELLED: Progress in structural biology depends on several key technologies. In particular tools for alignment and superposition of protein structures are indispensable. Here we describe the use of the TopMatch web service, an effective computational tool for protein structure alignment, for the visualization of structural similarities, and for highlighting relationships found in protein classifications. We provide several instructive examples. AVAILABILITY: TopMatch is available as a public web service at http://services.came.sbg.ac.at.

UNLABELLED: Three dimensional structures of proteins contain errors which often originate from limitations of the experimental techniques employed. Such errors frequently result in unfavorable atomic interactions. Here we present a new web service, called Interaction Viewer, for the visualization and correction of such errors. We show how the Interaction Viewer is used in combination with the NQ-Flipper service to spot strained asparagine and glutamine rotamers and we emphasize the convenience of this service in correcting such errors. AVAILABILITY: The web service is integrated with the NQ-Flipper service and accessible at http://flipper.services.came.sbg.ac.at

UNLABELLED: The database SCOP (Structural Classification Of Proteins) has become a major resource in bioinformatics and protein science. A particular strength of SCOP is the flexibility of its rules enabling the preservation of the many details spotted by experts in the classification process. Here we endow classic SCOP Families with quantified structural information and comment on the structural diversity found in the SCOP hierarchy. AVAILABILITY: Quantified SCOP (QSCOP) is available as a public WEB service. http://services.came.sbg.ac.at.

Abstract Summary: The error rate of asparagine (Asn) and glutamine (Gln) amide rotamers in protein crystal structures is in the order of 20% and as a consequence the current Protein Database (PDB) contains approximately half a million incorrect Asn and Gln side-chain rotamers. Here we present NQ-Flipper, a web service based on knowledge-based potentials of mean force to automatically detect and correct erroneous rotamers. We achieve excellent agreement with expert curated data. Availability: The program is accessible freely as a web service at Contact: [email protected]

Large-scale annotation of sets of proteins is a frequently occurring task in association with genome sequencing projects. Here, we present an automated platform for the functional annotation of large sets of protein sequences. Various bioinformatics tools are used to achieve a comprehensive description of protein sequences and to link these results to standard Gene Ontology descriptors for molecular function, biological processes and cellular components. Access to the annotation is provided via a web-interface and database queries. These interfaces allow to formulate proteome wide queries as well as the investigation of details of individual results. WILMA annotations of the proteomes of Homo sapiens, Mus musculus, Arabidopsis thaliana and Caenorhabditis elegans are accessible at http://www.came.sbg.ac.at/wilma/