Relationship Between Amino Acid Properties and Protein Compressibility

Compressibility is a property which characterizes the folded state of a globular protein critically. While the 20 amino acids themselves exhibit negative compressibility, the globular proteins exhibit positive compressibility. As the compressibility property of amino acids alone could not explain the compressibility property of proteins, in this work we incorporate 26 other properties of amino acids to explain protein compressibility. Of these, the 12 properties, thermodynamic transfer hydrophobicity, bulkiness, α-helix tendency, power to be at the N terminus of α helix, partial specific volume, solvent accessible reduction ratio, refractive index, molecular weight, compressibility, power to adopt (propensity) turn, power to adopt coil, and mean amplitude of fluctuation of constituent amino acids selected from single property relation, when incorporated in a multiple regression fit predict the adiabatic compressibility of proteins very satisfactorily. In general, protein compressibility seems to be determined to a great extent by the interior seeking seven residues, Ala, Phe, Ile, Leu, Val, Met and Trp. The predictive scheme performs far better than the already available techniques in the field. Additional factors that may influence the protein compressibility are indicated.