BACKGROUND: Hidden Markov Models power many state-of-the-art tools in the field of protein bioinformatics. While excelling in their tasks, these methods of protein analysis do not convey directly information on medium- and long-range residue-residue interactions. This requires an expressive power of at least context-free grammars. However, application of more powerful grammar formalisms to protein analysis has been surprisingly limited. RESULTS: In this work, we present a probabilistic grammatical framework for problem-specific protein languages and apply it to classification of transmembrane helix-helix pairs configurations. The core of the model consists of a probabilistic context-free grammar, automatically inferred by a genetic algorithm from only a generic set of expert-based rules and positive training samples. The model was applied to produce sequence based descriptors of four classes of transmembrane helix-helix contact site configurations. The highest performance of the classifiers reached AUCROC of 0.70. The analysis of grammar parse trees revealed the ability of representing structural features of helix-helix contact sites. CONCLUSIONS: We demonstrated that our probabilistic context-free framework for analysis of protein sequences outperforms the state of the art in the task of helix-helix contact site classification. However, this is achieved without necessarily requiring modeling long range dependencies between interacting residues. A significant feature of our approach is that grammar rules and parse trees are human-readable. Thus they could provide biologically meaningful information for molecular biologists.
BACKGROUND: Hidden Markov Models power many state-of-the-art tools in the field of protein bioinformatics. While excelling in their tasks, these methods of protein analysis do not convey directly information on medium- and long-range residue-residue interactions. This requires an expressive power of at least context-free grammars. However, application of more powerful grammar formalisms to protein analysis has been surprisingly limited. RESULTS: In this work, we present a probabilistic grammatical framework for problem-specific protein languages and apply it to classification of transmembrane helix-helix pairs configurations. The core of the model consists of a probabilistic context-free grammar, automatically inferred by a genetic algorithm from only a generic set of expert-based rules and positive training samples. The model was applied to produce sequence based descriptors of four classes of transmembrane helix-helix contact site configurations. The highest performance of the classifiers reached AUCROC of 0.70. The analysis of grammar parse trees revealed the ability of representing structural features of helix-helix contact sites. CONCLUSIONS: We demonstrated that our probabilistic context-free framework for analysis of protein sequences outperforms the state of the art in the task of helix-helix contact site classification. However, this is achieved without necessarily requiring modeling long range dependencies between interacting residues. A significant feature of our approach is that grammar rules and parse trees are human-readable. Thus they could provide biologically meaningful information for molecular biologists.
Authors: Christian J A Sigrist; Lorenzo Cerutti; Nicolas Hulo; Alexandre Gattiker; Laurent Falquet; Marco Pagni; Amos Bairoch; Philipp Bucher Journal: Brief Bioinform Date: 2002-09 Impact factor: 11.622
Authors: Marco Punta; Penny C Coggill; Ruth Y Eberhardt; Jaina Mistry; John Tate; Chris Boursnell; Ningze Pang; Kristoffer Forslund; Goran Ceric; Jody Clements; Andreas Heger; Liisa Holm; Erik L L Sonnhammer; Sean R Eddy; Alex Bateman; Robert D Finn Journal: Nucleic Acids Res Date: 2011-11-29 Impact factor: 16.971