Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10795910 | Biochimica et Biophysica Acta (BBA) - Bioenergetics | 2012 | 8 Pages |
Abstract
The purpose of the work was to provide a crystallographic demonstration of the venerable idea that CO photolyzed from ferrous heme-a3 moves to the nearby cuprous ion in the cytochrome c oxidases. Crystal structures of CO-bound cytochrome ba3-oxidase from Thermus thermophilus, determined at ~Â 2.8-3.2Â Ã
resolution, reveal a Fe-C distance of ~Â 2.0Â Ã
, a Cu-O distance of 2.4Â Ã
and a Fe-C-O angle of ~ 126°. Upon photodissociation at 100 K, X-ray structures indicate loss of Fea3-CO and appearance of CuB-CO having a Cu-C distance of ~ 1.9 Ã
and an O-Fe distance of ~Â 2.3Â Ã
. Absolute FTIR spectra recorded from single crystals of reduced ba3-CO that had not been exposed to X-ray radiation, showed several peaks around 1975 cmâ 1; after photolysis at 100 K, the absolute FTIR spectra also showed a significant peak at 2050 cmâ 1. Analysis of the 'light' minus 'dark' difference spectra showed four very sharp CO stretching bands at 1970 cmâ 1, 1977 cmâ 1, 1981 cmâ 1, and 1985 cmâ 1, previously assigned to the Fea3-CO complex, and a significantly broader CO stretching band centered at ~ 2050 cmâ 1, previously assigned to the CO stretching frequency of CuB bound CO. As expected for light propagating along the tetragonal axis of the P43212 space group, the single crystal spectra exhibit negligible dichroism. Absolute FTIR spectrometry of a CO-laden ba3 crystal, exposed to an amount of X-ray radiation required to obtain structural data sets before FTIR characterization, showed a significant signal due to photogenerated CO2 at 2337 cmâ 1 and one from traces of CO at 2133 cmâ 1; while bands associated with CO bound to either Fea3 or to CuB in “light” minus “dark” FTIR difference spectra shifted and broadened in response to X-ray exposure. In spite of considerable radiation damage to the crystals, both X-ray analysis at 2.8 and 3.2 Ã
and FTIR spectra support the long-held position that photolysis of Fea3-CO in cytochrome c oxidases leads to significant trapping of the CO on the CuB atom; Fea3 and CuB ligation, at the resolutions reported here, are otherwise unaltered. This article is part of a Special Issue entitled: Respiratory Oxidases.
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Authors
Bin Liu, Yang Zhang, J. Timothy Sage, S. Michael Soltis, Tzanko Doukov, Ying Chen, C. David Stout, James A. Fee,