CASP9 target classification

Lisa N. Kinch, Shuoyong Shi, Hua Cheng, Qian Cong, Jimin Pei, Valerio Mariani, Torsten Schwede, Nick V. Grishin

Research output: Contribution to journalArticlepeer-review

55 Scopus citations


The Critical assessment of protein structure prediction round 9 (CASP9) aimed to evaluate predictions for 129 experimentally determined protein structures. To assess tertiary structure predictions, these target structures were divided into domain-based evaluation units that were then classified into two assessment categories: template based modeling (TBM) and template free modeling (FM). CASP9 targets were split into domains of structurally compact evolutionary modules. For the targets with more than one defined domain, the decision to split structures into domains for evaluation was based on server performance. Target domains were categorized based on their evolutionary relatedness to existing templates as well as their difficulty levels indicated by server performance. Those target domains with sequence-related templates and high server prediction performance were classified as TMB, whereas those targets without identifiable templates and low server performance were classified as FM. However, using these generalizations for classification resulted in a blurred boundary between CASP9 assessment categories. Thus, the FM category included those domains without sequence detectable templates (25 target domains) as well as some domains with difficult to detect templates whose predictions were as poor as those without templates (five target domains). Several interesting examples are discussed, including targets with sequence related templates that exhibit unusual structural differences, targets with homologous or analogous structure templates that are not detectable by sequence, and targets with new folds.

Original languageEnglish (US)
Pages (from-to)21-36
Number of pages16
JournalProteins: Structure, Function and Bioinformatics
Issue numberSUPPL. 10
StatePublished - 2011


  • CASP9
  • Classification
  • Fold space
  • Free modeling
  • Protein structure
  • Sequence homologs
  • Structure analogs
  • Structure prediction
  • Template based modeling

ASJC Scopus subject areas

  • Structural Biology
  • Biochemistry
  • Molecular Biology


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