title: A statistical score for assessing the quality of multiple sequence alignments.
abstract: BACKGROUND
  Multiple sequence alignment is the foundation of many important applications in bioinformatics that aim at detecting functionally important regions, predicting protein structures, building phylogenetic trees etc. Although the automatic construction of a multiple sequence alignment for a set of remotely related sequences cause a very challenging and error-prone task, many downstream analyses still rely heavily on the accuracy of the alignments.
  
  
  RESULTS
  To address the need for an objective evaluation framework, we introduce a statistical score that assesses the quality of a given multiple sequence alignment. The quality assessment is based on counting the number of significantly conserved positions in the alignment using importance sampling method in conjunction with statistical profile analysis framework. We first evaluate a novel objective function used in the alignment quality score for measuring the positional conservation. The results for the Src homology 2 (SH2) domain, Ras-like proteins, peptidase M13, subtilase and beta-lactamase families demonstrate that the score can distinguish sequence patterns with different degrees of conservation. Secondly, we evaluate the quality of the alignments produced by several widely used multiple sequence alignment programs using a novel alignment quality score and a commonly used sum of pairs method. According to these results, the Mafft strategy L-INS-i outperforms the other methods, although the difference between the Probcons, TCoffee and Muscle is mostly insignificant. The novel alignment quality score provides similar results than the sum of pairs method.
  
  
  CONCLUSIONS
  The results indicate that the proposed statistical score is useful in assessing the quality of multiple sequence alignments.
authors.affiliation: Biotechnology and Food Research, MTT Agrifood Research Finland, Jokioinen, Finland. virpi.ahola@mtt.fi
authors.forename: Virpi
authors.initials: V
authors.lastname: Ahola
authors.forename: Tero
authors.initials: T
authors.lastname: Aittokallio
authors.forename: Mauno
authors.initials: M
authors.lastname: Vihinen
authors.forename: Esa
authors.initials: E
authors.lastname: Uusipaikka
mesh_terms: D000465:Algorithms; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D019295:Computational Biology / Q000379:methods*; D003198:Computer Simulation; D003627:Data Interpretation, Statistical; D015233:Models, Statistical; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D012984:Software