Moments of the distribution of the amino acid residues in tertiary structures of globular proteins

Moments of the distributions of the C^α and “side-chain atoms” and associated properties were examined in 22 globular proteins, considered as statistical aggregates of atoms. Although the distributions are generally anisotropic, the densities of the evaluated distributions are highly uniform in the interior of a single protein, as well as among the proteins investigated. The tertiary structure of proteins is characterized by a compact and uniform distribution of amino acids, independent of their molecular weight and hydrophobic character, and by an isotropic distribution of the virtual bond directions in the polypeptide folding. While the general uniformity of the density of distributions in the bulk of proteins can be justified by the architectural requirements of high thermodynamic stability, significant differences in the distribution of the C^α with respect to the “side-chain atoms” suggest a plausible explanation of the general anisotropic morphology of the proteins. The invariance of the density of distributions allows easy recognition of proteinlike domains in more complex proteins and suggests a practical way to predict the following path in single proteins.