Crystal structure of decameric 2-Cys peroxiredoxin from human erythrocytesat 1.7 angstrom resolution

Background: The peroxiredoxins (Prxs) are an emerging family of multifuncti onal enzymes that exhibit peroxidase activity in vitro, and in vivo partici pate in a range of cellular processes known to be sensitive to reactive oxy gen species. Thioredoxin peroxidase B (TPx-B), a 2-Cys type II Prx from ery throcytes, promotes potassium efflux and down-regulates apoptosis and the r ecruitment of monocytes by endothelial tissue. Results: The crystal structure of human decameric TPx-B purified from eryth rocytes has been determined to 1.7 resolution. The structure is a toroid co mprising five dimers linked end-on through predominantly hydrophobic intera ctions, and is proposed to represent an intermediate in the in vivo reactio n cycle. In the crystal structure, Cys51, the site of peroxide reduction, i s oxidised to cysteine sulphinic acid. Cys 172, the second catalytic cystei ne residue, lies similar to 10 away from Cys51 and in this conformation of TPx-B is too distant to recycle the activity of Cys51. Conclusions: The oxidation of Cys51 appears to have trapped the structure i nto a stable decamer, as confirmed by sedimentation analysis. A comparison with two previously reported dimeric Prx structures reveals that the cataly tic cycle of 2-Cys Prx requires significant conformational changes that inc lude the unwinding of the active-site helix and the movement of four loops. It is proposed that the stable decamer forms in vivo under conditions of o xidative stress. Similar decameric structures of TPx-B have been observed b y electron microscopy, which show the protein associated with the erythrocy te membrane.