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A needle in a haystack: the active site of the membrane-bound complex cytochrome c nitrite reductase, Almeida, M. G., Silveira C. M., Guigliarelli B., Bertrand P., Moura J. J., Moura I., and Leger C. , FEBS Lett, Jan 23, Volume 581, Number 2, p.284-8, (2007) AbstractWebsite

Cytochrome c nitrite reductase is a multicenter enzyme that uses a five-coordinated heme to perform the six-electron reduction of nitrite to ammonium. In the sulfate reducing bacterium Desulfovibrio desulfuricans ATCC 27774, the enzyme is purified as a NrfA2NrfH complex that houses 14 hemes. The number of closely-spaced hemes in this enzyme and the magnetic interactions between them make it very difficult to study the active site by using traditional spectroscopic approaches such as EPR or UV-Vis. Here, we use both catalytic and non-catalytic protein film voltammetry to simply and unambiguously determine the reduction potential of the catalytic heme over a wide range of pH and we demonstrate that proton transfer is coupled to electron transfer at the active site.

Predicting Protein-Protein Interactions Using BiGGER: Case Studies, Almeida, R. M., Dell'Acqua S., Krippahl L., Moura J. J. G., and Pauleta S. R. , Molecules, Volume 21, p.1037, (2016) Website
Gd(III) chelates as NMR probes of protein-protein interactions. Case study: rubredoxin and cytochrome c3, Almeida, R. M., Geraldes C. F., Pauleta S. R., and Moura J. J. , Inorg Chem, Nov 7, Volume 50, Number 21, p.10600-7, (2011) AbstractWebsite

Two cyclen-derived Gd probes, [Gd-DOTAM](3+) and [Gd-DOTP](5-) (DOTAM = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetamide; DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylenephosphonate)), were assessed as paramagnetic relaxation enhancement (PRE)-inducing probes for characterization of protein-protein interactions. Two proteins, Desulfovibrio gigas rubredoxin and Desulfovibrio gigas cytochrome c(3), were used as model partners. In a (1)H NMR titration it was shown that [Gd-DOTP](5-) binds to cytochrome c(3) near heme IV, causing pronounced PREs, characterized by line width broadenings of the heme methyl resonances at ratios as low as 0.08. A K(d) of 23 +/- 1 muM was calculated based on chemical shift perturbation of selected heme methyl resonances belonging to three different heme groups, caused by allosteric effects upon [Gd-DOTP](5-) binding to cytochrome c(3) at a molar ratio of 2. The other probe, [Gd-DOTAM](3+), caused PREs on a well-defined patch near the metal center of rubredoxin (especially the patch constituted by residues D19-G23 and W37-S45, which broaden beyond detection). This effect was partially reversed for some resonances (C6-Y11, in particular) when cytochrome c(3) was added to this system. Both probes were successful in causing reversible PREs at the partner binding site, thus showing to be good probes to identify partners' binding sites and since the interaction is reversible to structurally characterize protein complexes by better defining the complex interface.

Using cytochrome c(3) to make selenium nanowires, Abdelouas, A., Gong W. L., Lutze W., Shelnutt J. A., Franco R., and Moura I. , Chemistry of Materials, Jun, Volume 12, Number 6, p.1510-+, (2000) AbstractWebsite

We report on a new method to make nanostructures in aqueous solution at room temperature. We used the protein cytochrome c(3) to catalyze reduction of selenate (SeO42-) to selenium Se-0 by dithionite. Reduction was instantaneous. After a week spherical nanoparticles of red Se-0 (about 50 nm diameter) precipitated, followed by self-assembling into crystalline nanowires, typically 1 mu m long. The nanowires were composed of one strand of spherical particles; thicker strands contained several nanoparticles in parallel.

Cooperative use of cytochrome cd1 nitrite reductase and its redox partner cytochrome c552 to Improve the selectivity of nitrite biosensing, A.S., Serra, S. Jorge, C. Silveira, J.J.G. Moura, E. Jubete, E. Ochoteco, and G. Almeida M. , Anal Chim Acta, Volume 693, p.41-46, (2011)