Article

The chemistry of the CuB site in cytochrome c oxidase and the importance of its unique His-Tyr bond.

Helsinki Bioenergetics Group, Programme of Structural Biology and Biophysics, Institute of Biotechnology, University of Helsinki, Helsinki, Finland.
Biochimica et Biophysica Acta (Impact Factor: 4.66). 05/2009; 1787(4):221-33. DOI: 10.1016/j.bbabio.2009.01.002
Source: PubMed

ABSTRACT The CuB metal center is at the core of the active site of the heme-copper oxidases, comprising a copper atom ligating three histidine residues one of which is covalently bonded to a tyrosine residue. Using quantum chemical methodology, we have studied the CuB site in several redox and ligand states proposed to be intermediates of the catalytic cycle. The importance of the His-Tyr crosslink was investigated by comparing energetics, charge, and spin distributions between systems with and without the crosslink. The His-Tyr bond was shown to decrease the proton affinity and increase the electron affinity of both Tyr-244 and the copper. A previously unnoticed internal electronic equilibrium between the copper atom and the tyrosine was observed, which seems to be coupled to the unique structure of the system. In certain states the copper and Tyr-244 compete for the unpaired electron, the localization of which is determined by the oxygenous ligand of the copper. This electronic equilibrium was found to be sensitive to the presence of a positive charge 10 A away from the center, simulating the effect of Lys-319 in the K-pathway of proton transfer. The combined results provide an explanation for why the heme-copper oxidases need two pathways of proton uptake, and why the K-pathway is active only in the second half of the reaction cycle.

0 Bookmarks
 · 
76 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Gram-positive bacteria are decorated by a variety of proteins that are anchored to the cell wall and project from it to mediate colonization, attachment to host cells, and pathogenesis. These proteins, and protein assemblies, such as pili, are typically long and thin yet must withstand high levels of mechanical stress and proteolytic attack. The recent discovery of intramolecular isopeptide bond cross-links, formed autocatalytically, in the pili from Streptococcus pyogenes has highlighted the role that such cross-links can play in stabilizing such structures. We have investigated a putative cell-surface adhesin from Clostridium perfringens comprising an N-terminal adhesin domain followed by 11 repeat domains. The crystal structure of a two-domain fragment shows that each domain has an IgG-like fold and contains an unprecedented ester bond joining Thr and Gln side chains. MS confirms the presence of these bonds. We show that the bonds form through an autocatalytic intramolecular reaction catalyzed by an adjacent His residue in a serine protease-like mechanism. Two buried acidic residues assist in the reaction. By mutagenesis, we show that loss of the ester bond reduces the thermal stability drastically and increases susceptibility to proteolysis. As in pilin domains, the bonds are placed at a strategic position joining the first and last strands, even though the Ig fold type differs. Bioinformatic analysis suggests that similar domains and ester bond cross-links are widespread in Gram-positive bacterial adhesins.
    Proceedings of the National Academy of Sciences 12/2013; · 9.81 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Transition metal ion complexation with proteins is ubiquitous across such diverse fields as neurodegenerative and cardiovascular diseases and cancer. In this study, the structures of divalent copper ion centers including three histidine and one oxygen-ligated amino acid residues and the relative binding affinities of the oxygen-ligated amino acid residues with these metal ion centers, which are debated in the literature, are presented. Furthermore, new force field parameters, which are currently lacking for the full-length metal-ligand moieties, are developed for metalloproteins that have these centers. These new force field parameters enable investigations of metalloproteins possessing these binding sites using molecular simulations. In addition, the impact of using the atom equivalence and inequivalence atomic partial charge calculation procedures on the simulated structures of these metallopeptides, including hydration properties, is described. © 2014 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 04/2014; · 3.84 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The reaction of oxidized bovine cytochrome c oxidase (bCcO) with hydrogen peroxide (H(2)O(2)) was studied by electron paramagnetic resonance (EPR) to determine the properties of radical intermediates. Two distinct radicals with widths of 12 and 46 G are directly observed by X-band EPR in the reaction of bCcO with H(2)O(2) at pH 6 and pH 8. High-frequency EPR (D-band) provides assignments to tyrosine for both radicals based on well-resolved g-tensors. The wide radical (46 G) exhibits g-values similar to a radical generated on L-Tyr by UV-irradiation and to tyrosyl radicals identified in many other enzyme systems. In contrast, the g-values of the narrow radical (12 G) deviate from L-Tyr in a trend akin to the radicals on tyrosines with substitutions at the ortho position. X-band EPR demonstrates that the two tyrosyl radicals differ in the orientation of their β-methylene protons. The 12 G wide radical has minimal hyperfine structure and can be fit using parameters unique to the post-translationally modified Y244 in bCcO. The 46 G wide radical has extensive hyperfine structure and can be fit with parameters consistent with Y129. The results are supported by mixed quantum mechanics and molecular mechanics calculations. In addition to providing spectroscopic evidence of a radical formed on the post-translationally modified tyrosine in CcO, this study resolves the much debated controversy of whether the wide radical seen at low pH in the bovine enzyme is a tyrosine or tryptophan. The possible role of radical formation and migration in proton translocation is discussed.
    Journal of the American Chemical Society 03/2012; 134(10):4753-61. · 10.68 Impact Factor

Full-text (2 Sources)

View
5 Downloads
Available from
May 19, 2014