Oligonucleotides antiviral drugs have been actively used in medicine over the last decades, but the molecular mechanism of their action remains unclear. The RNA-based drug is known to increase interferon production and stimulate nonspecific antiviral protection. As shown in our previous works, the combination of oligonucleotides with alcoholic sugar D-mannitol leads to changes in their biological activity and efficiency.
We studied the interactions between Interferon α2b and mononucleotides (NMP), yeast oligoribonucleotides (ORNs), their Na+ salts (ORNsNa), and complex with Dmannitol (ORNs:DM). To investigate the interaction and conformational changes of IFN with ligands the quenching and lifetime of fluorescence, circular dichroism spectroscopies and isothermal titration calorimetry (ITC) were used.
The most active quenching and decrease INF, when titrated with NMPs and ORNs, was obtained using acid forms in combination with mannitol lifetime of fluorescence. The quenching and lifetime of fluorescence INF when titrated saline forms slightly different from control. Thus, when using the ORN:DM, quenching was 28%. INF has a lifetime of 2.95 ns, after interacting with ORN and ORN:D-M INF has a fluorescence lifetime of 2.37 and 2.32 ns, respectively. The quenching and lifetime of fluorescence INF when titrated AMP:DM - 17% and 1.92 ns, respectively, GMP:DM - 45% and 2.53 ns, CMP:D-M - 42% and 2.24ns, UMP:D-M - 13% and 2.25 ns. The analysis of the IFN secondary structure by Bestsel shows the decrease in the structure of the number of secondary elements when interacting between INF and acidic forms nucleotides. On the other hand, an increase in the number of secondary elements in the interaction between INF and salt forms NMPs and ORNs were obtained. The ITC curves titration of INF with ORNs and NMPs indicate that the reaction of the interaction between protein and acidic ligands is exothermic and with saline endothermically. It is known that exothermic protein-ligand interaction increases the conformational mobility of the protein and endothermic decrease.
Different effects of different forms of ORNs and NMPs on the secondary structure of the INF can be explained by various binding sites. The ORNs and ribonucleotides have the advantage of interacting with proteins, unlike salt ORNs and nucleotide monophosphates, because they have a stronger binding. Thus, we assume the same compound in various forms may act as an inhibitor and activator for the protein. To test this assumption in the case of nucleotide ligands, we plan to conduct studies with the interferon receptor.