Interaction of 5’–ribonucleoside monophosphates with Interferon α–2b

Aim.To characterize by different approaches the interaction of Interferon -2b (IFN -2b) with cytidine 5'-monophophosphoric acid (5'-CMP), guanosine 5'-monophophosphoric acid (5'-GMP), uridine 5'-monophophosphoric acid (5'-UMP) and their disodium salts, in the presence and absence of D-mannitol.Methods.Spectroscopy (time-resolved, circular dichroism and fluorescence), isothermal nanocalorimetry.Results.Using IFN -2b intrinsic fluorescence measurements we established that 5'-GMP and 5'-CMP interact with IFN -2b stronger than their disodium salts while no difference of affinity was observed for 5'-UMP and its disodium salt.The presence of D-mannitol enhances the observed effects for 5'-GMP and 5'-CMP, but not for their disodium salts and all forms of 5'-UMP.Thermodynamic measurements reveal that the interaction of all tested 5'-ribonucleoside monophosphoric acids with IFN -2b are exothermic, while of all disodium salt of 5'-ribonucleoside monophosphates are endothermic.The entropy factor TS was calculated to be negative in the presence of all 5'-ribonu-cleoside monophosphoric acids indicating a decrease of randomness in the system and positive in the presence of their disodium salts indicating an opposite effect.Circular dichroism measurements showed that 5'-ribonucleoside monophosphoric acids induce a decrease of the regular alpha helices content and increase the unstructured regions length in INF -2b.In contrast, their disodium salts make rather stabilizing effect on the secondary structure elements of the protein.Conclusions.5'-ribonucleoside monophosphoric acids used in this study interact with IFN -2b in different way compared to their disodium salts.Acid forms of 5'-ribonucleoside monophosphates possess higher affinity to IFN -2b and destabilize secondary structure elements of this protein.This may restrain a conformational mobility of IFN -2b and as a consequence modify its functional activity.In contrast, disodium salts of 5'-ribonucleoside monophosphates display a weak affinity to IFN -2b and stabilize its secondary structure organization.