The spatial distribution of physical, chemical, energetic and conformational properties of amino acid residues in globular proteins

An attempt is made to obtain information as to the spatial distribution of amino acid residues in globular proteins in terms of their chemical, physical, energetic and conformational properties. The crystallographic data on twenty-one protein molecules form the basis for the study. The properties of the residues, namely, hydrophobicity, polarity, acidity, molecular weight, bulkness, chromatographic index, refractivity, short/medium/long-range energetics, and powers to adopt a-helical, extended and bend structures are analysed by dividing the protein globule into six concentric shells containing equal numbers of residues. The results show that the decisive factor in determining the spatial position of a residue in a protein molecule is of composite nature involving a compromise between the various properties of the residue. The observed deviations from the general hydrophobic interior and hydrophilic exterior in globular proteins are nicely brought out. A valuable clue is obtained as to the directional properties of α-helical and extended structure segments in proteins. The relative buried, exposed and intermediate characters of the residues in protein globules are obtained in a very realistic approach.