title: Frequency of dipeptides and antidipeptides.
abstract: Although it is reasonable to expect that the frequency of a generic dipeptide XY in proteins is the same of its counterpart YX, on the basis of an accurate statistical analysis of a large number of protein sequences, it appears that some dipeptides XY are considerably more frequent than their mirror images YX, referred to as antidipeptides. Given that it has been verified that this unexpected anisotropic frequency of occurrence is unbiased by the type of protein sequences that are analyzed, it is possible to conclude that this is a genuine phenomenon. Nevertheless, it was impossible to find the mechanism underlying this unexpected phenomenon, which does not seem to be related to diverse conformational propensities, to the different conformational flexibility of the peptide/antidipeptide pair, to dissimilar accessibility to the solvent or to gene random mutations.
authors.affiliation: Department of Chemistry, University of Pavia, viale Taramelli12, I-27100 Pavia, Italy ; Department of Structural and Computational Biology, Max F. Perutz Laboratories, Vienna University, Campus Vienna Biocenter 5, A-1030 Vienna, Austria.
authors.forename: Oliviero
authors.initials: O
authors.lastname: Carugo
keywords: Amino acid composition; Antidipeptide; Dipeptide; Protein sequence