Determination of Intrinsic Hydrophilicity/Hydrophobicity Coefficients of Amino Acid Side-Chains using Synthetic Model Peptides

摘要

The concept of hydrophobicity has been a topic of much study in all aspects of science. It is most important in the hydrophobic effect, as exemplified by the relative hydrophilicity/hydrophobicity of amino acid side-chains and how they interact, which is the most important factor underlying the hierarchical structure, function, and stability of proteins. The measurement of amino acid side-chain hydrophilicity/hydrophobicity has been carried out by a number of approaches, both chromatographic and non-chromatographic, described in an excellent review by Biswas et al. Despite there being over one hundred scales in the literature, there is not a good consensus in ranking or value for all side-chains. Certainly, we believe that scales to date are useful; however, a definitive "intrinsic" set of coefficients has yet to be determined. "Intrinsic" implies the maximum hydrophilicity/ hydrophobicity of side-chains in a peptide chain in the absence of nearest-neighbor effects (i to i ± 1 side-chain interactions) and/or any restriction of rotational freedom of the peptide chain that prevents full expression of the side-chain hydrophilicity/ hydrophobicity. Our approach uses reversed-phase high-performance liquid chromatography (RP-HPLC) to separate mixtures of synthetic de novo designed model peptides which contain 23 single amino acid substitutions, encompassing the 20 naturally occurring amino acids plus norvaline, norleucine, and ornithine. From the observed retention behavior of these model peptides, we have obtained intrinsic coefficient values at three pH values over six mobile phase conditions.