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FragBag, an accurate representation of protein structure, retrieves structural neighbors from the entire PDB quickly and accurately.

ABSTRACT: Fast identification of protein structures that are similar to a specified query structure in the entire Protein Data Bank (PDB) is fundamental in structure and function prediction. We present FragBag: An ultrafast and accurate method for comparing protein structures. We describe a protein structure by the collection of its overlapping short contiguous backbone segments, and discretize this set using a library of fragments. Then, we succinctly represent the protein as a "bags-of-fragments"-a vector that counts the number of occurrences of each fragment-and measure the similarity between two structures by the similarity between their vectors. Our representation has two additional benefits: (i) it can be used to construct an inverted index, for implementing a fast structural search engine of the entire PDB, and (ii) one can specify a structure as a collection of substructures, without combining them into a single structure; this is valuable for structure prediction, when there are reliable predictions only of parts of the protein. We use receiver operating characteristic curve analysis to quantify the success of FragBag in identifying neighbor candidate sets in a dataset of over 2,900 structures. The gold standard is the set of neighbors found by six state of the art structural aligners. Our best FragBag library finds more accurate candidate sets than the three other filter methods: The SGM, PRIDE, and a method by Zotenko et al. More interestingly, FragBag performs on a par with the computationally expensive, yet highly trusted structural aligners STRUCTAL and CE.

SUBMITTER: Budowski-Tal I

PROVIDER: S-EPMC2840415 | biostudies-literature | 2010 Feb

REPOSITORIES: biostudies-literature

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FragBag, an accurate representation of protein structure, retrieves structural neighbors from the entire PDB quickly and accurately.

Budowski-Tal Inbal I Nov Yuval Y Kolodny Rachel R

Proceedings of the National Academy of Sciences of the United States of America 20100203 8

Fast identification of protein structures that are similar to a specified query structure in the entire Protein Data Bank (PDB) is fundamental in structure and function prediction. We present FragBag: An ultrafast and accurate method for comparing protein structures. We describe a protein structure by the collection of its overlapping short contiguous backbone segments, and discretize this set using a library of fragments. Then, we succinctly represent the protein as a "bags-of-fragments"-a vect ...[more]

PMID: 20133727

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Project description:BACKGROUND: Since RNA molecules regulate genes and control alternative splicing by allostery, it is important to develop algorithms to predict RNA conformational switches. Some tools, such as paRNAss, RNAshapes and RNAbor, can be used to predict potential conformational switches; nevertheless, no existent tool can detect general (i.e., not family specific) entire riboswitches (both aptamer and expression platform) with accuracy. Thus, the development of additional algorithms to detect conformational switches seems important, especially since the difference in free energy between the two metastable secondary structures may be as large as 15-20 kcal/mol. It has recently emerged that RNA secondary structure can be more accurately predicted by computing the maximum expected accuracy (MEA) structure, rather than the minimum free energy (MFE) structure. RESULTS: Given an arbitrary RNA secondary structure S? for an RNA nucleotide sequence a = a?,..., a(n), we say that another secondary structure S of a is a k-neighbor of S?, if the base pair distance between S? and S is k. In this paper, we prove that the Boltzmann probability of all k-neighbors of the minimum free energy structure S? can be approximated with accuracy ? and confidence 1 - p, simultaneously for all 0 ? k < K, by a relative frequency count over N sampled structures, provided that N>N(?,p,K)=??¹(p/2K)²/4?², where ?(z) is the cumulative distribution function (CDF) for the standard normal distribution. We go on to describe the algorithm RNAborMEA, which for an arbitrary initial structure S? and for all values 0 ? k < K, computes the secondary structure MEA(k), having maximum expected accuracy over all k-neighbors of S?. Computation time is O(n³ · K²), and memory requirements are O(n² · K). We analyze a sample TPP riboswitch, and apply our algorithm to the class of purine riboswitches. CONCLUSIONS: The approximation of RNAbor by sampling, with rigorous bound on accuracy, together with the computation of maximum expected accuracy k-neighbors by RNAborMEA, provide additional tools toward conformational switch detection. Results from RNAborMEA are quite distinct from other tools, such as RNAbor, RNAshapes and paRNAss, hence may provide orthogonal information when looking for suboptimal structures or conformational switches. Source code for RNAborMEA can be downloaded from http://sourceforge.net/projects/rnabormea/ or http://bioinformatics.bc.edu/clotelab/RNAborMEA/.

Dataset Information

FragBag, an accurate representation of protein structure, retrieves structural neighbors from the entire PDB quickly and accurately.

Publications

FragBag, an accurate representation of protein structure, retrieves structural neighbors from the entire PDB quickly and accurately.

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