Distances and classification of amino acids for different protein secondary structures.

Window profiles of amino acids in protein sequences are used to describe the amino acid environment. The relative entropy or Kullback-Leibler distance derived from these profiles is used as a measure of dissimilarity for comparison of amino acids and secondary structure conformations. Distance matrices of amino acid pairs at different conformations are obtained, which display a non-negligible dependence of amino acid similarity on conformations. Based on the conformation specific distances, a clustering analysis for amino acids is conducted.