E.O. Mikhajlova, A.R. Kayumov, O.A. Markelov, A.A. Khamidullina, L.R. Khisameeva, M.I. Bogachev

The pathogenicity is a genetically determined property of microorganisms to cause disease in the host. Pathogenicity of bacteria is determined by factors of pathogenicity, including extracellular enzymes, factors of adhesion and invasion, immune evasion and toxins. Toxins are natural facilities of bacteria in environmental adaptation and surviving. The purpose of this study was to analyze the structure of toxins produced by pathogenic microorganisms in order to identify common structural elements. Since the toxins from different bacteria have a similar effect on the same molecular target in a cell, theoretically, they must possess highly homologous functional domains demonstrating biological activity. The regions with high similarity have been identified among the toxins of different functional groups. Despite the identification of probable functional domains which usually consist of 2-3 amino acids, the homology between the toxins of different bacteria species is almost absent (5-10%) even within the functional class. To evaluate the statistical similarity between different toxin groups with a similar biological effect, but differing in the primary structure of the molecule, we analyzed their multifractal properties by return interval statistics approach. The analysis has shown significant differences in the qualitative composition of amino acids with stretched distributions for a toxins in Gram-negative and gram-positive bacteria. No correlation between amino acid residues located in the predicted functional domains and residues that determine the multifractal properties of the molecule have been observed. Their functional and evolutionary significance of these features remain unknown. Perhaps their position is more important for the structure formation of the molecule than for its biological activity.