Interaction between alpha-2-macroglobulin and phycocyanobilin – structural and physiological implications

Abstract

The interaction between phycocyanobilin (PCB), a bioactive chromophore of blue-green cyanobacteria Spirulina’s phycobiliproteins, and human alpha-2-macroglobulin (a2M), a universal anti-proteinase, was investigated in this study under simulated physiological conditions using spectroscopic techniques and a2M activity assay. Protein a2M was found to bind PCB with a moderate affinity, as assessed by spectrofluorimetric titration. The binding constant was calculated to be 6.39105 M 1 at 25°C. The binding of PCB to a2M did not cause significant change in the secondary structure of the protein, as determined by circular dichroism. PCB protected a2M from oxidative damage in the presence of AAPH-induced free radical overproduction. PCB binding also effectively preserved a2M anti-proteinase activity. Since a2M is involved in controlling the action of enzymes during the inflammatory process, the protection that PCB expresses could indirectly influence the intensity and direction of the body response to impaired homeostasis, especially under oxidative stress.