o:25904 Nutraceutical phycocyanobilin binding to catalase protects the pigment from oxidation without affecting catalytic activity Vezivanje nutricionističkog fikocijanobilina za katalazu štiti pigment od oksidacije bez uticaja na katalaznu aktivnost en ABSTRACT Phycocyanobilin is a dark blue linear tetrapyrrole chromophore covalently attached to protein subunits of phycobiliproteins present in the light-harvesting complexes of the cyanobacteria Arthrospira platensis (Spirulina "superfood"). It shows exceptional health-promoting properties and emerging use in various fields of bioscience and industry. This study aims to examine the mutual impact of phycocyanobilin interactions with catalase, a life-essential antioxidant enzyme. Fluorescence quenching experiments demonstrated moderate binding (Ka of 3.9 × 10 4 M-1 at 25 °C; n = 0.89) (static type), while van't Hoff plot points to an enthalpically driven ligand binding (ΔG = -28.2 kJ mol-1; ΔH = -41.9 kJ mol-1). No significant changes in protein secondary structures (α-helix content ~22%) and thermal protein stability in terms of enzyme tetramer subunits (Tm ~ 64 °C) were detected upon ligand binding. Alterations in the tertiary catalase structure were found without adverse effects on enzyme activity (~2 × 10 6 IU/mL). The docking study results indicated that the ligand most likely binds to amino acid residues (Asn141, Arg362, Tyr369 and Asn384) near the cavity between the enzyme homotetramer subunits not related to the active site. Finally, complex formation protects the pigment from free-radical induced oxidation (bleaching), suggesting possible prolongation of its half-life and bioactivity in vivo if bound to catalase. Sažetak activity, binding, catalase, phycocyanobilin, structure 1552099 10.1016/j.saa.2021.119483 2022-06-03T13:30:45.105Z 44 yes 46 Nikola Gligorijević University of Belgrade, Institute for the Application of Nuclear Energy INEP, Serbia doktor biohemijskih nauka 0000-0002-8691-2486 Milan R. Nikolić University of Belgrade, Faculty of Chemistry, Department of Biochemistry & Center of Excellence for Molecular Food Sciences, Serbia person Theodore G. Sotiroudis National Hellenic Research Foundation, Institute of Chemical Biology, Athens, Greece person Olgica Nedić University of Belgrade, Institute for the Application of Nuclear Energy INEP, Serbia doktor biohemijskih nauka person 0000-0003-2042-0056 Vassiliki Papadimitriou National Hellenic Research Foundation, Institute of Chemical Biology, Athens, Greece person Milica Radibratović University of Belgrade, Institute of Chemistry, Technology and Metallurgy, Department of Chemistry, Serbia person Simeon Minić University of Belgrade, Faculty of Chemistry, Department of Biochemistry & Center of Excellence for Molecular Food Sciences, Serbia person application/pdf 75649 https://phaidrabg.bg.ac.rs/o:25904 no yes 1 70 92000001 11A29 11A2905 11A19 11A1903 11A24 11A2404 Spectrochimica Acta-Part A: Molecular and Biomolecular Spectroscopy 251 Elsevier 2021