o:30859 Phycocyanobilin is a new binding partner of human alpha-2-macroglobulin that protects the protein against oxidative stress Fikocijanobilin je novi vezujući partner alfa-2-makroglobulina čoveka koji štiti protein od oksidativnog stresa en ABSTRACT Under simulated physiological conditions, this study investigates the interaction between nutraceutical phycocyanobilin (PCB) and the universal anti-protease protein human alpha-2-macroglobulin (α2M). Extensive molecular docking analyses on multiple α2M conformations, spectroscopic techniques, and α2M activity assays were utilized to examine the complex formation. The results revealed that for every protein conformation, two high energy binding sites exist: the first, conformationally independent, at the interface region between two monomer chains and the second, conformationally dependent, in the pocket composed of amino acids from four distinct domains (TED, RBD, CUB, and MG2) of the single protein chain. Spectrofluorimetric measurements indicated a moderate affinity between α2M and PCB with a moderately high binding constant of 6.3 × 10 5 M−1 at 25 °C. The binding of PCB to α2M resulted in minor changes in the secondary structure content of α2M. Furthermore, PCB protected α2M from oxidation and preserved its anti-protease activity in the oxidative environment. These findings suggest that PCB binding could indirectly impact the body’s response to oxidative stress by influencing α2M's role in controlling enzyme activity during the inflammatory process. Alpha-2-macroglobulin, phycocyanobilin, protein-ligand interactions, docking, spectroscopy 1552099 10.1080/07391102.2023.2248273 2023-09-20T07:22:41.365Z 44 yes 46 Miloš Šunderić University of Belgrade, Institute for the Application of Nuclear Energy INEP, Serbia doktor biohemijskih nauka 0000-0002-0940-9481 Nikola Gligorijević Department of Chemistry, Institute of Chemistry, Technology, and Metallurgy, National Institute of the Republic of Serbia, University of Belgrade, Serbia person Miloš Milčić Department of General and Inorganic Chemistry, Faculty of Chemistry, University of Belgrade, Serbia person Simeon Minić Department of Biochemistry and Center of Excellence for Molecular Food Sciences, Faculty of Chemistry, University of Belgrade, Serbia person Olgica Nedić University of Belgrade, Institute for the Application of Nuclear Energy INEP, Serbia doktor biohemijskih nauka person 0000-0003-2042-0056 Milan Nikolić Department of Biochemistry and Center of Excellence for Molecular Food Sciences, Faculty of Chemistry, University of Belgrade, Serbia person application/pdf 61365 https://phaidrabg.bg.ac.rs/o:30859 no yes 1 70 92000001 11A29 11A2905 11A24 11A2404 11A19 Journal of Biomolecular Structure and Dynamics Taylor&Francis Group 2023