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

Abstract

In this study, the interaction between phycocyanobilin (PCB)1, a bioactive chromophore of blue-green algae Spirulina's phycobiliproteins, and alpha-2-macroglobulin (α2M)2, a universal anti-proteinase, was investigated under simulated physiological conditions using spectroscopic techniques and α2M activity assay. Using spectrofluorimetric measurements, we found that α2M binds PCB with a moderate affinity, with a binding constant of 6.3× 105 M−1 at 25°C. The binding of PCB to α2M does not cause any significant change in the secondary structure of the protein (circular dichroism measurements). Besides, PCB protects α2M from structural oxidative alterations under AAPH-induced free radical overproduction. Further, PCB binding effectively preserves α2M anti-proteinase activity. Since α2M 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 body response to impaired homeostasis, especially under oxidative stress.