ИСТИНА

Glycation is a non-enzymatic reaction between sugars and proteins being especially effective in the diabetic patient’s blood. The reaction leads to modification of the amino groups of arginine and lysine through forming of a Schiff base and an Amadori product. Since these residues play a key role in electrostatic interaction with other proteins, nucleic acids and other natural charged molecules, we have investigated the effect of glycation on the interaction of natural and synthetic polyelectrolytes with protein. We used unstructured protein beta-casein, glycation agent was methylglyoxal. The interaction between glycated and native beta-casein with polyelectrolytes has been investigated. Polycation poly(alkylvinylpyridinium) and polianions heparin, polycytosine, poly(styrenesulfonate) (PSS), poly(methacrylic acid) and polyacrylic acid were used. The size of native and modified casein, as well as complexes with polyelectrolytes, was measured by dynamic light scattering and analytical ultracentrifugation at different temperatures. Casein, depending on the temperature, is monomer or forms micelles. Monomer and micelles of casein interacted only with PSS. Glycated casein was apt to form large aggregates, but the binding of the protein with some polyelectrolytes resulted in the form of complexes comparable in size with monomer of the protein. Using isothermal titration calorimetry, it was shown that the native protein bound to polyelectrolytes more active than glycated protein. Furthermore, micelles of casein interacted more strongly with polyelectrolytes than monomer. According to the data of circular dichroism, glycation, temperature and the interaction with polyelectrolytes did not affect on the secondary structure of casein. The effect of polymers on the proteolysis of native and glycated casein was investigated. It turned out that the addition of polyelectrolytes protected the protein from proteolysis. A model was proposed that explains observed results and the influence of polyelectrolyte properties on the interaction with native and modified casein. Furthermore, the influence of model polyelectrolytes on the interaction of casein with other proteins was studied. It has been already shown that the addition of glycated casein to denatured glyceraldehyde 3-phosphate dehydrogenase (GAPDH) causes aggregation of the last, but native casein does not cause aggregation. The addition of polyelectrolytes to the GAPDH was completely suppressed the aggregation caused by glycated casein. Obtained results contribute to the better understanding of the interaction mechanisms of glycated proteins with various polyelectrolytes, in particular, nucleic acids. This work is financially supported by RSCF (grant № 16-14-10027).