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iFC2: an integrated web-server for improved prediction of protein structural class, fold type, and secondary structure content

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Abstract

Several descriptors of protein structure at the sequence and residue levels have been recently proposed. They are widely adopted in the analysis and prediction of structural and functional characteristics of proteins. Numerous in silico methods have been developed for sequence-based prediction of these descriptors. However, many of them do not have a public web-server and only a few integrate multiple descriptors to improve the predictions. We introduce iFC2 (integrated prediction of fold, class, and content) server that is the first to integrate three modern predictors of sequence-level descriptors. They concern fold type (PFRES), structural class (SCEC), and secondary structure content (PSSC-core). The server exploits relations between the three descriptors to implement a cross-evaluation procedure that improves over the predictions of the individual methods. The iFC2 annotates fold and class predictions as potentially correct/incorrect. When tested on datasets with low-similarity chains, for the fold prediction iFC2 labels 82% of the PFRES predictions as correct and the accuracy of these predictions equals 72%. The accuracy of the remaining 28% of the PFRES predictions equals 38%. Similarly, our server assigns correct labels for over 79% of SCEC predictions, which are shown to be 98% accurate, while the remaining SCEC predictions are only 15% accurate. These results are shown to be competitive when contrasted against recent relevant web-servers. Predictions on CASP8 targets show that the content predicted by iFC2 is competitive when compared with the content computed from the tertiary structures predicted by three best-performing methods in CASP8. The iFC2 server is available at http://biomine.ece.ualberta.ca/1D/1D.html.

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Abbreviations

CASP:

Critical assessment of techniques for protein structure prediction

FASTA:

FAST-all

iFC2 :

Integrated prediction of fold class and content

iFC2-FT:

iFC2 cross-evaluation for fold type

iFC2-SSC:

iFC2 cross-evaluation for secondary structure content

iFC2-SC:

iFC2 cross-evaluation for structural class

MAE:

Mean absolute error

PSSM:

Position-specific scoring matrix

PSSC-core:

Prediction of secondary structure content through comprehensive sequence representation

SCEC:

Prediction of structural class using evolutionary collocation

PDB:

Protein data bank

PFRES:

Protein fold recognition using evolutionary information and predicted secondary structure

SCOP:

Structural classification of proteins

SVM:

Support vector machine

3D:

Tertiary

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Acknowledgments

KC and WS research was supported by the Alberta Ingenuity and iCORE Scholarships. LK acknowledges support from NSERC Canada.

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Correspondence to Lukasz Kurgan.

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Chen, K., Stach, W., Homaeian, L. et al. iFC2: an integrated web-server for improved prediction of protein structural class, fold type, and secondary structure content. Amino Acids 40, 963–973 (2011). https://doi.org/10.1007/s00726-010-0721-1

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