Structural changes in cytochrome c oxidase induced by cytochrome c binding. A resonance Raman study

Electrostatically stabilized complexes of fully oxidized cytochrome c oxida se from Paracoccus denitrificans and horse heart cytochrome c were studied by resonance Raman spectroscopy. The experiments were carried out with the wild-type oxidase and a variant in which a negatively charged amino acid in the binding domain (D257) is replaced by an asparagine. It is shown that c ytochrome c induces structural changes at heme a and heme a(3) which are re miniscent to those found in mammalian cytochrome c oxidase-cytochrome c com plex. The spectral changes are attributed to subtle changes in the hemeprot ein interactions implying that there is a structural communication from the binding domain even to the remote catalytic center. Only for the heme a mo des minor spectral differences were found in the response of the wild-type and the D257N variant oxidase upon cytochrome c binding indicating that ele ctrostatic interactions of aspartate 257 are not crucial for the perturbati on of the catalytic site structure in the complex. On the other hand, in no ne of the complexes, structural changes were detected in the bound cytochro me c. These findings are in contrast to previous results obtained with beef heart cytochrome c oxidase which triggers the formation of a new conformat ional state of cytochrome c assumed to be involved in the biological electr on transfer process. (C) 2000 Elsevier Science B.V. All rights reserved.