This Article Full Text Full Text (PDF) Supplemental material Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Coronado, J. E. Articles by Lipke, P. N. Search for Related Content PubMed PubMed Citation Articles by Coronado, J. E. Articles by Lipke, P. N.

Composition-Modified Matrices Improve Identification of Homologs of Saccharomyces cerevisiae Low-Complexity Glycoproteins

Department of Biological Sciences and Center for Gene Structure and Function, Hunter College of City University of New York, New York, New York 10021,¹ Department of Computer Science, Hunter College of City University of New York, New York, New York 10021²

Received 25 September 2005/ Accepted 1 February 2006

Yeast glycoproteins are representative of low-complexity sequences, those sequences rich in a few types of amino acids. Low-complexity protein sequences comprise more than 10% of the proteome but are poorly aligned by existing methods. Under default conditions, BLAST and FASTA use the scoring matrix BLOSUM62, which is optimized for sequences with diverse amino acid compositions. Because low-complexity sequences are rich in a few amino acids, these tools tend to align the most common residues in nonhomologous positions, thereby generating anomalously high scores, deviations from the expected extreme value distribution, and small e values. This anomalous scoring prevents BLOSUM62-based BLAST and FASTA from identifying correct homologs for proteins with low-complexity sequences, including Saccharomyces cerevisiae wall proteins. We have devised and empirically tested scoring matrices that compensate for the overrepresentation of some amino acids in any query sequence in different ways. These matrices were tested for sensitivity in finding true homologs, discrimination against nonhomologous and random sequences, conformance to the extreme value distribution, and accuracy of e values. Of the tested matrices, the two best matrices (called E and gtQ) gave reliable alignments in BLAST and FASTA searches, identified a consistent set of paralogs of the yeast cell wall test set proteins, and improved the consistency of secondary structure predictions for cell wall proteins.

Supplemental material for this article may be found at http://ec.asm.org/.

This article has been cited by other articles:

• Coronado, J. E., Mneimneh, S., Epstein, S. L., Qiu, W.-G., Lipke, P. N. (2007). Conserved Processes and Lineage-Specific Proteins in Fungal Cell Wall Evolution. Eukaryot Cell 6: 2269-2277 [Abstract] [Full Text]