Conformational, Fluorescence and Energy Parameters of Interferon α2b with Different Forms of Oligoribonucleotides and Adenosine Monophosphate ^†

(1) Background: It is known that RNA in Na⁺ salt form has only immunomodulatory activity, and in acid form additionally acquires anti-inflammatory activity and in combination with D-mannitol acquires an even broader antiviral effect. The study aimed to study the ability of adenosinmonophosphat (AMP) and oligoribonucleotides (ORNs) in acid and salt form and in combination with D-mannitol to affect the conformation and fluorescence of interferon (INF) α-2b and to determine the energy parameters of these interactions. (2) Methods: spectroscopy (time pulsed and fluorescence), isothermal nanocalorimetry. (3) Results: AMP and ORNs in acid form and complex with D-mannitol bind more strongly to interferon α-2b than salt analogues. In the interaction of interferon α-2b and acid AMP and especially in complex with D-mannitol, the reaction occurs exothermically and change in conformational mobility INF by increasing the content of disordered regions. When INF α-2b interacts with salt AMP, the reaction occurs endothermically, and probably the salt form increases the conformational stiffness of INF α-2b. The greater efficiency of nonradiative energy transfer from INF α-2b to acid AMP has been shown, due to the closer distance between molecules. (4) Conclusions: AMP in acid form interacts more actively and increases the conformational mobility of INF, at a greater relative distance and with less Gibbs energy compared to the salt form, which probably causes the appearance of additional biological properties of acidic AMP.