Two-dimensional classification of interfacial and partitioning properties of amino acids

Abstract: A classification of amino acid residues based on the interfacial and partitioning properties was introduced by Khokhlov et al. [1] [2] Amino acid residues are characterized by two parameters: the standard free energy of adsorption of an amino acid at an octanol/water interface and the standard free energy of the partition of an amino acid between octanol and water, both of them normalized by kT. As a result, five groups of amino acids having similar values of the parameters are identified. This classification for the amino acids is based in trace correlations between two one-dimensional parameters which are related with the interactions in the biological environment: hydrophilic / hydrophobic behaviour (partition) and activity at the interface (surface tension). This method is believed to be able to provide promising results in the search of correlation giving rise to protein sequences. A comparison of the parameters in question gives information on energetic preferences of the molecules to be located at the interface or in a bulk phase. This study is applied on serine, threonine, aspartic acid, glutamic acid and tyrosine.