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From Protein Structure to Function with Bioinformatics.pdf

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100 T. Nugent and D.T. JonesTable 4.3 Machine learning-based alpha-helical TM <strong>to</strong>pology predic<strong>to</strong>rs. MSA: Topology predictionsmade using multiple sequence alignments. HGA: Suitable for whole genome analysisMethod URL Algorithm FeaturesMEMSAT3 http://bioinf.cs.ucl.ac.uk/psipred/ NN Signal peptide,MSA, HGAMINNOU http://minnou.cchmc.org/ NN MSAPHDhtm http://www.predictprotein.org/ NN Signal peptide,MSA, constrainedPhobius http://phobius.sbc.su.se/ HMM HGATMHMMhttp://www.cbs.dtu.dk/services/TMHMM/HMM Re-entrantregion, HGAPRODIV-TMHMM http://www.pdc.kth.se/~hakanv/ HMM Constrainedprodiv-tmhmm/HMMTOP http://www.enzim.hu/hmm<strong>to</strong>p/ HMM MSAENSEMBLE http://pongo.biocomp.unibo. NN + HMM Re-entrant regionit/pongo/OCTOPUS http://oc<strong>to</strong>pus.cbr.su.se/ NN + HMM ConsensusSVM<strong>to</strong>phttp://bio-cluster.iis.sinica.edu. SVM Consensustw/~bioapp/SVM<strong>to</strong>p/PONGOhttp://pongo.biocomp.unibo. Multipleit/pongo/BPROMPT http://www.jenner.ac.uk/bprompt/ MultipleMore recently, Support Vec<strong>to</strong>r Machines (SVMs) have been applied <strong>to</strong> TM protein<strong>to</strong>pology prediction (Yuan et al. 2004; Lo et al. 2008). While NNs and HMMsare capable of producing multiple outputs, SVMs are binary classifiers thereforemultiple SVMs must be employed <strong>to</strong> classify the numerous residue preferencesbefore being combined in<strong>to</strong> a probabilistic framework. Although multiclass rankingSVMs do exist, they are generally considered unreliable since in many cases nosingle mathematical function exists <strong>to</strong> separate all classes of data from one another.However, SVMs are capable of learning complex relationships among the aminoacids <strong>with</strong>in a given window <strong>with</strong> which they are trained, particularly when provided<strong>with</strong> evolutionary information, and are also more resilient <strong>to</strong> the problem ofover-training compared <strong>to</strong> other machine learning methods, although numerousadjustable parameters can result in optimisation becoming extremely timeconsuming.4.6.1.2 Consensus ApproachesA number of methods now combine multiple machine learning approaches.ENSEMBLE (Martelli et al. 2003) uses a NN and two HMMs, while OCTOPUS(Viklund and Elofsson 2008) uses two sets of four NNs and one HMM. Both groupsreport higher prediction accuracies compared <strong>with</strong> methods based on only a single

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