Journal Article

A probabilistic approach to protein backbone tracing in electron density maps

Frank DiMaio, Jude Shavlik and George N. Phillips

in Bioinformatics

Volume 22, issue 14, pages e81-e89
Published in print July 2006 | ISSN: 1367-4803
Published online July 2006 | e-ISSN: 1460-2059 | DOI:
A probabilistic approach to protein backbone tracing in electron density maps

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One particularly time-consuming step in protein crystallography is interpreting the electron density map; that is, fitting a complete molecular model of the protein into a 3D image of the protein produced by the crystallographic process. In poor-quality electron density maps, the interpretation may require a significant amount of a crystallographer's time. Our work investigates automating the time-consuming initial backbone trace in poor-quality density maps. We describe ACMI (Automatic Crystallographic Map Interpreter), which uses a probabilistic model known as a Markov field to represent the protein. Residues of the protein are modeled as nodes in a graph, while edges model pairwise structural interactions. Modeling the protein in this manner allows the model to be flexible, considering an almost infinite number of possible conformations, while rejecting any that are physically impossible. Using an efficient algorithm for approximate inference—belief propagation—allows the most probable trace of the protein's backbone through the density map to be determined. We test ACMI on a set of ten protein density maps (at 2.5 to 4.0 Å resolution), and compare our results to alternative approaches. At these resolutions, ACMI offers a more accurate backbone trace than current approaches.

Journal Article.  0 words. 

Subjects: Bioinformatics and Computational Biology

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