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Evaluation of PSI-BLAST alignment accuracy in comparison to structural alignments
I Friedberg1, T Kaplan, H Margalit
1Department of Molecular Genetics and Biotechnology, The Hebrew University, Hadassah Medical School, Jerusalem, Israel.
Protein Science : a Publication of the Protein Society
|January 11, 2001
Summary
The PSI-BLAST algorithm accurately detects remote protein evolutionary relationships. Its alignment accuracy improves over iterations, reaching 50.9% sensitivity in detecting structurally similar but sequence-dissimilar protein pairs.
Area of Science:
- Bioinformatics
- Computational Biology
- Structural Biology
Background:
- Protein sequence analysis is key for understanding protein function and evolution.
- PSI-BLAST is a powerful tool for identifying remote evolutionary relationships using sequence data alone.
- Accurate sequence alignment is critical for homology modeling and structural prediction.
Purpose of the Study:
- To rigorously assess the accuracy of PSI-BLAST sequence alignments.
- To evaluate PSI-BLAST's performance on structurally similar yet sequence-dissimilar protein pairs.
- To quantify alignment sensitivity and specificity over multiple PSI-BLAST iterations.
Main Methods:
- A stringent database of 123 structurally similar, sequence-dissimilar protein pairs was curated.
- PSI-BLAST was used to compare each protein sequence against a non-redundant sequence database.
- Alignment accuracy was determined by comparing PSI-BLAST alignments to structure-based alignments.
Main Results:
- PSI-BLAST successfully detected pair-mates for 52 out of 123 protein pairs.
- The average alignment sensitivity was 43.5% ± 2.2% compared to structural alignments.
- Alignment sensitivity improved across consecutive iterations, reaching 50.9% ± 2.5% by the fifth iteration.
Conclusions:
- PSI-BLAST demonstrates significant capability in detecting remote evolutionary relationships.
- Alignment accuracy, measured by sensitivity, shows improvement with iterative refinement.
- The study validates PSI-BLAST's utility for identifying homologous proteins with low sequence identity.