Oligomer-dependent heme-binding to human peroxiredoxin 1

Peroxiredoxin 1 (PRX1) is a member of the peroxiredoxin family, a ubiquitous group of thiol-based peroxidases with high reactivity toward hydrogen peroxide. Human peroxiredoxin 1 (PRX1) exists in equilibrium between monomeric, dimeric, and decameric forms. In our previous study (Watanabe et al., 2017, Biochem. Biophys. Res. Commun.483, 930-935), we found that monomeric PRX1 binds heme through Cys52. Because Cys52 is the active center of PRX1, heme binding results in an almost complete loss of peroxidase activity. In this study, we investigated the effects of heme on the decameric form of PRX1, the most active and abundant form in the cytoplasm. Spectroscopic titration demonstrated that decameric PRX1 binds one heme per subunit with a dissociation constant of 2.3 ± 1.9 μM. UV-vis spectra of heme-bound decameric PRX1 suggest histidine coordination to heme rather than cysteine coordination. In contrast to the monomeric form, heme binding to decameric PRX1 enhanced peroxidase activity by approximately 2-fold and also protected heme from H₂O₂-induced degradation. Under oxidizing conditions, heme binding shifts the oligomeric equilibrium toward the decamer form. Collectively, our results indicate that decameric PRX1 plays a key role in protecting heme by sheltering it from H₂O₂ and serves to control antioxidant activity upon heme binding.