title: Sequence variation in ligand binding sites in proteins.
abstract: BACKGROUND
  The recent explosion in the availability of complete genome sequences has led to the cataloging of tens of thousands of new proteins and putative proteins. Many of these proteins can be structurally or functionally categorized from sequence conservation alone. In contrast, little attention has been given to the meaning of poorly-conserved sites in families of proteins, which are typically assumed to be of little structural or functional importance.
  
  
  RESULTS
  Recently, using statistical free energy analysis of tetratricopeptide repeat (TPR) domains, we observed that positions in contact with peptide ligands are more variable than surface positions in general. Here we show that statistical analysis of TPRs, ankyrin repeats, Cys2His2 zinc fingers and PDZ domains accurately identifies specificity-determining positions by their sequence variation. Sequence variation is measured as deviation from a neutral reference state, and we present probabilistic and information theory formalisms that improve upon recently suggested methods such as statistical free energies and sequence entropies.
  
  
  CONCLUSIONS
  Sequence variation has been used to identify functionally-important residues in four selected protein families. With TPRs and ankyrin repeats, protein families that bind highly diverse ligands, the effect is so pronounced that sequence "hypervariation" alone can be used to predict ligand binding sites.
authors.affiliation: Department of Molecular Biophysics & Biochemistry, Yale University, PO Box 208114, New Haven, CT 06520-8114, USA. magliery@chemistry.ohio-state.edu
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Magliery
authors.forename: Lynne
authors.initials: L
authors.lastname: Regan
mesh_terms: D001665:Binding Sites; D017124:Conserved Sequence; D008024:Ligands; D009687:Nuclear Proteins / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D011956:Receptors, Cell Surface / Q000378:metabolism*; D012091:Repetitive Sequences, Nucleic Acid / Q000235:genetics*; D020539:Sequence Analysis, Protein / Q000379:methods*
chemical_list: D008024:Ligands; D009687:Nuclear Proteins; D010455:Peptides; D011956:Receptors, Cell Surface