Protein topology classification using two-stage support vector machines

Genome Inform. 2006;17(2):259-69.

Abstract

The determination of the first 3-D model of a protein from its sequence alone is a non-trivial problem. The first 3-D model is the key to the molecular replacement method of solving phase problem in x-ray crystallography. If the sequence identity is more than 30%, homology modelling can be used to determine the correct topology (as defined by CATH) or fold (as defined by SCOP). If the sequence identity is less than 25%, however, the task is very challenging. In this paper we address the topology classification of proteins with sequence identity of less than 25%. The input information to the system is amino acid sequence, the predicted secondary structure and the predicted real value relative solvent accessibility. A two stage support vector machine (SVM) approach is proposed for classifying the sequences to three different structural classes (alpha, beta, alpha+beta) in the first stage and 39 topologies in the second stage. The method is evaluated using a newly curated dataset from CATH with maximum pairwise sequence identity less than 25%. An impressive overall accuracy of 87.44% and 83.15% is reported for class and topology prediction, respectively. In the class prediction stage, a sensitivity of 0.77 and a specificity of 0.91 is obtained. Data file, SVM implementation (SVMHEAVY) and result files can be downloaded from http://www.ee.unimelb.edu.au/ISSNIP/downloads/.

MeSH terms

  • Amino Acid Sequence
  • Crystallography, X-Ray
  • Databases, Factual
  • Evolution, Molecular
  • Molecular Sequence Data
  • Predictive Value of Tests
  • Protein Conformation*
  • Protein Folding
  • Protein Structure, Secondary
  • Proteins / chemistry*
  • Proteins / classification*
  • Reproducibility of Results
  • Sensitivity and Specificity
  • Sequence Alignment / methods
  • Sequence Analysis, Protein
  • Software
  • Solvents / chemistry
  • Thermodynamics

Substances

  • Proteins
  • Solvents