STATISTICAL ANALYSIS OF DISTRIBUTION OF AMINO ACID RESIDUES AMONG HELICAL AND NON-HELICAL REGIONS IN GLOBULAR PROTEINS

A statistical analysis of the distribution of different amino acid residues among helical and non-helical regions of seven globular proteins: myoglobin, α-and β-haemoglobin, lysozyme, ribonuclease, α-chymotrypsin and papain, has been made. It was found that the distribution of a number of amino acid residues differs essentially from the distribution averaged over all amino acids. Hydrophobic amino acids-alanine and leucine-show a tendency to occupy internal turns of helical regions. Negatively and positively charged amino acids have a tendency to concentrate, correspondingly, at the amino- and carbonyl-ends of helical regions. Amino acids with hetero-atoms (O or S atoms) near the main chain (serine, threonine, cystine, asparagine) have a tendency to concentrate in non-helical regions (including the regions with β-structure). Proline can be located either on the amino-ends of helical regions or in non-helical regions. The regularities found correlate with properties of the corresponding synthetic polypeptides and can be explained on the basis of the influence of hydrophobic, electrostatic and sterical interactions on the secondary structure of polypeptide chains. A check was made of Guzzo's and Prothero's empirical rules concerning the relationship between the amino acid composition of the given region of the polypeptide chain and its secondary structure, and it was shown that Guzzo's rule is in disagreement with the results of statistical analysis, whereas Prothero's rule agrees with them. © 1969.