Phycocyanobilin is a new binding partner of human alpha-2-macroglobulin that protects the protein against oxidative stress.

Under simulated physiological conditions, this study investigates the interaction between nutraceutical phycocyanobilin (PCB) and the universal anti-protease protein human alpha-2-macroglobulin (αM). 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 αM and PCB with a moderately high binding constant of 6.3 10 M at 25 °C. The binding of PCB to αM resulted in minor changes in the secondary structure content of αM. Furthermore, PCB protected αM 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 αM's role in controlling enzyme activity during the inflammatory process.Communicated by Ramaswamy H. Sarma.