The crystal structure of the iron-free cytochrome c peroxidase and its implication for the enzymatic mechanism.

We report the refined structure of an iron-free form of cytochrome c peroxidase (CcP) at 2.3 A resolution. The backbone comparison between native CcP and iron-free CcP shows that the two structures have the same protein fold within experimental error. The only difference noted is in the heme pocket where the distance between the proximal histidine and the center of the protoporphyrin has increased. The results show that the iron-free CcP should be a good substitute for native CcP in fluorescence studies and thus also validate previous studies using iron-free CcPs as efficient fluorescent probes in electron transfer studies.