Improved Catenated Structures of Bovine Peroxiredoxin III F190L Reveal Details of Ring-Ring Interactions and a Novel Conformational State.

Mitochondrial 2-cys peroxiredoxin III (PrxIII) is a key player in antioxidant defence reducing locally-generated H2O2 to H2O. A Phe to Leu (F190L) mutation in the C-terminal α-helix of PrxIII, mimicking that found in some bacteria and parasites, increases its resistance to hyperoxidation but has no obvious influence on peroxidase activity. Here we report on the oxidized and reduced crystal structures of bovine PrxIII F190L at 2.4 A and 2.2 A, respectively. Both structures exist as two-ring catenanes with their dodecameric rings inclined at 55o to each other, similar to that previously reported for PrxIII C168S. The new higher-resolution structures reveal details of the complex network of H-bonds stabilising the inter-toroid contacts. In addition, Arg123, the key conserved residue, that normally interacts with the catalytic cys (Cp, cys 47) is found in a distinct conformation extending away from the Cp while the characteristic Arg-Glu-Arg network, underpinning the active-site geometry also displays a distinctive arrangement, not observed previously. This novel active-site organisation may provide new insights into the dynamics of the large-scale conformational changes occurring between oxidized and reduced states.