title: Fast subcellular localization by cascaded fusion of signal-based and homology-based methods.
abstract: BACKGROUND
  The functions of proteins are closely related to their subcellular locations. In the post-genomics era, the amount of gene and protein data grows exponentially, which necessitates the prediction of subcellular localization by computational means.
  
  
  RESULTS
  This paper proposes mitigating the computation burden of alignment-based approaches to subcellular localization prediction by a cascaded fusion of cleavage site prediction and profile alignment. Specifically, the informative segments of protein sequences are identified by a cleavage site predictor using the information in their N-terminal shorting signals. Then, the sequences are truncated at the cleavage site positions, and the shortened sequences are passed to PSI-BLAST for computing their profiles. Subcellular localization are subsequently predicted by a profile-to-profile alignment support-vector-machine (SVM) classifier. To further reduce the training and recognition time of the classifier, the SVM classifier is replaced by a new kernel method based on the perturbational discriminant analysis (PDA).
  
  
  CONCLUSIONS
  Experimental results on a new dataset based on Swiss-Prot Release 57.5 show that the method can make use of the best property of signal- and homology-based approaches and can attain an accuracy comparable to that achieved by using full-length sequences. Analysis of profile-alignment score matrices suggest that both profile creation time and profile alignment time can be reduced without significant reduction in subcellular localization accuracy. It was found that PDA enjoys a short training time as compared to the conventional SVM. We advocate that the method will be important for biologists to conduct large-scale protein annotation or for bioinformaticians to perform preliminary investigations on new algorithms that involve pairwise alignments.
authors.affiliation: Department of Electronic and Information Engineering, The Hong Kong Polytechnic University, Hong Kong. enmwmak@polyu.edu.hk.
authors.forename: Man-Wai
authors.initials: MW
authors.lastname: Mak
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Sun-Yuan
authors.initials: SY
authors.lastname: Kung