Search

Photoinduced charge-transfer dynamics and the influence of cluster size on the dynamics were investigated using five iron-sulfur clusters: the 1Fe-4S cluster in Pyrococcus furiosus rubredoxin, the 2Fe-2S cluster in Pseudomonas putida putidaredoxin, the 4Fe-4S cluster in nitrogenase iron protein, and the 8Fe-7S P-cluster and the 7Fe-9S-1Mo FeMo cofactor in nitrogenase MoFe protein. Laser excitation promotes the iron-sulfur clusters to excited electronic states that relax to lower states. The electronic relaxation lifetimes of the 1Fe-4S, 8Fe-7S, and 7Fe-9S-1Mo clusters are on the picosecond time scale, although the dynamics of the MoFe protein is a mixture of the dynamics of the latter two clusters. The lifetimes of the 2Fe-2S and 4Fe-4S clusters, however, extend to several nanoseconds. A competition between reorganization energies and the density of electronic states (thus electronic coupling between states) mediates the charge-transfer lifetimes, with the 2Fe-2S cluster of Pdx and the 4Fe-4S cluster of Fe protein lying at the optimum leading to them having significantly longer lifetimes. Their long lifetimes make them the optimal candidates for long-range electron transfer and as external photosensitizers for other photoactivated chemical reactions like solar hydrogen production. Potential electron-transfer and hole-transfer pathways that possibly facilitate these charge transfers are proposed.

Cyanide is added to oxidized 1Fe and 2Fe superoxide reductase (SOR) for the putative ferric-(hydro)peroxo intermediate in the reaction of the enzymes with superoxide by using vibrational and ENDOR spectroscopies to study the properties of the active site paramagnetic iron center. Low temperature ENDOR data shows that the bound cyanide adopts three distinct conformations in Fe(III)-CN SOR.

Resonance Raman results indicate that the electron transfer from rubredoxin to the mononuclear iron active site is mediated via superexchange pathways. Data show extensive coupling between the iron-sulfur stretching mode and the vibrational mode of cysteine.

Results reveal that the hydrogen bond network contributed by the first 15 amino acid residues of aporubredoxin or their interaction with other parts of the protein confer thermostability to the bacterial apo- and holoaporubredoxins.

Research has been conducted on the blue non-heme iron protein superoxide reductase (SOR). The investigation of the crystal structure of SOR in the oxidized and reduced forms is described.

The c-type cytochrome, cyt c(y), which is a photooxidized reactor center reduction pathway for Rhodobacter capsulatus, is the electron carrier that allows soluble cyt c2-independent photosynthetic growth. The cyt c(y) is observed in bc1 complex-lacking strains in a minimal, rather than rich, growth medium.

The solution structure of the PF0610, which is a novel winged helix-turn-helix (wHTH) protein with a rubredoxin-like Zn ribbon as its W1 segment, is determined by using nuclear magnetic resonance (NMR). The novel structure might help in understanding the transcription regulatory processes in Pyrococcus furiosus.

The ferrodoxin (Fd) of the Pyrococcus furiosus is distinct from other Fds derived from hyperthermophilic bacteria since it exhibits a number of rare properties. The Fd of these archaeon strains were found to possess a highly-stable molecular heterogeneity, an Asp cluster ligand and a flexible disulfide bond. Although other hyperthermophilic archaea a 13-member alpha helix bond, that of Pyrococcus furiosus feature a number of extensions which lead to the formation of tertiary contacts.

PF0610, a protein from the hyperthermophile Pyrococcus furiosus, has homologues only in other archaeal species and in three species of Fe(III)-reducing bacteria. It is thought to have a helix-turn-helix (HTH) domain at the N-terminus and possesses two CXXC motifs characteristic of metal binding proteins. We have determined the solution structure of the Zn-bound protein using NMR. PF0610 is a novel winged helix-turn-helix (wHTH) protein with a rubredoxin-like Zn ribbon as its W1 segment. In addition, it possesses a large number of basic residues on its surface. Clusters of basic residues can be found on both helix H3 and the metal-binding loops of W1, suggesting that it might be a DNA-binding protein. Accordingly, gel shift assays using both linear and circular DNA showed that PF0610 does bind DNA, at least in a sequence-independent fashion. Modeling the PF0610-DNA interaction based on other wHTH protein-DNA structures revealed that besides helix H3, basic residues around the second CXXC motif in the metal-binding loop could make extensive contacts with DNA. However, the bulkiness of the W1 region implies that the DNA conformation may be distorted upon PF0610 binding. PF0610 is the first protein known to have a Zn ribbon-embedded wHTH fold and, as such, has potential roles both as a metal-dependent transcription regulator and as a component of the chromosome packing system in P. furiosus. The discovery of this novel structure represents the addition of another branch to the winged HTH protein family and could contribute to our understanding of transcription regulatory processes in P. furiosus.