title: Nh3D: a reference dataset of non-homologous protein structures.
abstract: BACKGROUND
  The statistical analysis of protein structures requires datasets in which structural features can be considered independently distributed, i.e. not related through common ancestry, and that fulfil minimal requirements regarding the experimental quality of the structures it contains. However, non-redundant datasets based on sequence similarity invariably contain distantly related homologues. Here we provide a reference dataset of non-homologous protein domains, assuming that structural dissimilarity at the topology level is incompatible with recognizable common ancestry. The dataset is based on domains at the Topology level of the CATH database which hierarchically classifies all protein structures. It contains the best refined representatives of each Topology level, validates structural dissimilarity and removes internally duplicated fragments. The compilation of Nh3D is fully scripted.
  
  
  RESULTS
  The current Nh3D list contains 570 domains with a total of 90780 residues. It covers more than 70% of folds at the Topology level of the CATH database and represents more than 90% of the structures in the PDB that have been classified by CATH. We observe that even though all protein pairs are structurally dissimilar, some pairwise sequence identities after global alignment are greater than 30%.
  
  
  CONCLUSIONS
  Nh3D is freely available as a reference dataset for the statistical analysis of sequence and structure features of proteins in the PDB. Regularly updated versions of Nh3D and the corresponding PDB-formatted coordinate sets are accessible from our Web site http://www.schematikon.org.
authors: Department of Biochemistry, University of Toronto, 1 Kings College Circle, Toronto, Ontario M5S 1A8, Canada. b.thiruvahindrapuram@utoronto.ca
authors: B
authors: B
authors: Thiruv
authors: G
authors: G
authors: Quon
authors: S A
authors: SA
authors: Saldanha
authors: B
authors: B
authors: Steipe
mesh_terms: D000465:Algorithms; D002138:Calibration; D030562:Databases, Protein; D004220:Disulfides / Q000737:chemistry; D006801:Humans; D020407:Internet; D015233:Models, Statistical; D009502:Neutrons; D011487:Protein Conformation; D015202:Protein Engineering; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry*; D016415:Sequence Alignment; D040681:Structural Homology, Protein; D013329:Structure-Activity Relationship; D014961:X-Ray Diffraction
chemical_list: D004220:Disulfides; D011506:Proteins