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Discovery of novel protein families in metagenomic samples
Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. (Sonnhammer)
Department of Cell and Molecular Biology, Karolinska Institutet.
Department of Microbiology, Tumor- and Cell Biology, Karolinska Institutet.
Department of Cell and Molecular Biology, Karolinska Institutet.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Despite the steady rise in gene sequence information, there is a persistent, significant fraction of genes which do not match any previously known sequence. These genes are called ORFans, and metagenomic samples, where DNA is extracted from a mixed population of unknown and often uncultivable species, are a rich source of ORFans. Viral infections cause significant morbidity and mortality, and identifying ORFan viral gene families from human metagenomic samples represents a route to understanding molecular processes that affect human health. Few methods exist for metagenomic gene-finding, and most of them rely on sequence similarity, which cannot be used to detect ORFans. Furthermore, nonsimilarity-based methods are hard to apply to the complex mixture of short, higherror-rate sequence fragments which are typical of metagenomic projects. Here we present an approach to detect ORFan protein families in short-read data, and apply it to 937 Mbp (megabase pairs) of sequence from 17 virus-enriched libraries made from human nasopharyngeal aspirates, serum, feces, and cerebrospinal fluid samples. After isolating approximately 450 putative ORFan families from clusters of sequence contigs, we applied RNAcode, a gene finder developed for use on high-quality genome sequences, and calibrated it for errorprone short sequence reads. Additional predictive measures such as sequence complexity and length were then used to rank and filter candidates into a high-quality set of 32 putative novel gene families, only two of which show significant similarity to known genes.

Keywords [en]
metagenomics, novel genes, human virome, gene prediction
National Category
Bioinformatics and Systems Biology
Identifiers
URN: urn:nbn:se:su:diva-75107OAI: oai:DiVA.org:su-75107DiVA, id: diva2:514207
Available from: 2012-04-10 Created: 2012-04-05 Last updated: 2022-02-24Bibliographically approved
In thesis
1. Biological data exchange and the discovery of new protein families in metagenomic samples
Open this publication in new window or tab >>Biological data exchange and the discovery of new protein families in metagenomic samples
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The rise in sequence data has brought both challenges to the way we exchange biological information and opportunities to discover new protein families, primarily through the investigation of uncultured metagenomic samples.The Distributed Annotation System, or DAS, provided a means for exchanging protein sequence data, but there were no open source, stand-alone DAS clients optimized for integrating and viewing these data. To address this need, we developed DASher. Complementary to visualizing DAS data with DASher, we also created and made available ten servers to offer real-time protein feature predictions via DAS. While DAS works well for genomic data, there was no such framework for exchanging orthology data in a consistent way. Consequently, we developed the first standards for orthology data exchange, SeqXML and OrthoXML. 64 reference proteomes are now available in SeqXML, and 14 orthology providers have agreed to offer their predictions in OrthoXML. Besides creating a uniform representation of common data types, these standards enable direct comparison and assessment of competing methods for the first time.A substantial percentage of newly sequenced genes are ORFans, which have no match to previously known sequences. Metagenomics samples uncover sequences from uncultivable and therefore previously unseen species, and ORFans constitute much of the metagenomics data that are completely uncharacterized. ORFans are by definition impervious to standard similarity-based methods, and the few existing metagenomics gene-finding methods performed poorly on short, error-prone next-generation sequence data. Therefore, we designed a new approach to predict protein-coding gene families from metagenomic data and applied it to 17 virally-enriched metagenomes derived from human patients. Of the 456 putative ORFan families we found in the nearly 1 billion nucleotides sequenced from these libraries, we identified 32 putative novel protein families with strong support.

Place, publisher, year, edition, pages
Stockholm: Department of Biochemistry and Biophysics, Stockholm University, 2012. p. 124
National Category
Bioinformatics and Systems Biology
Research subject
Biochemistry with Emphasis on Theoretical Chemistry
Identifiers
urn:nbn:se:su:diva-75108 (URN)978-91-74474-52-7 (ISBN)
Public defence
2012-05-11, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:30 (English)
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Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2012-04-19 Created: 2012-04-05 Last updated: 2022-02-24Bibliographically approved

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Messina, DavidSonnhammer, Erik

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