Structural and spectropotentiometric analysis of Blastochloris viridis heterodimer mutant reaction center

Heterodimer mutant reaction centers (RCs) of Blastochloris viridis were crystallized using microfluidic technology. In this mutant, a leucine residue replaced the histidine residue which had acted as a fifth ligand to the bacteriochlorophyll (BChl) of the primary electron donor dimer M site (HisM200). With the loss of the histidine-coordinated Mg, one bacteriochlorophyll of the special pair was converted into a bacteriopheophytin (BPhe), and the primary donor became a heterodimer supermolecule. The crystals had dimensions 400 × 100 ×100 μm, belonged to space group P43212, and were isomorphous to the ones reported earlier for the wild type (WT) strain. The structure was solved to a 2.5 Å resolution limit. Electron-density maps confirmed the replacement of the histidine residue and the absence of Mg. Structural changes in the heterodimer mutant RC relative to the WT included the absence of the water molecule that is typically positioned between the M side of the primary donor and the accessory BChl, a slight shift in the position of amino acids surrounding the site of the mutation, and the rotation of the M194 phenylalanine. The cytochrome subunit was anchored similarly as in the WT and had no detectable changes in its overall position. The highly conserved tyrosine L162, located between the primary donor and the highest potential heme C380, revealed only a minor deviation of its hydroxyl group. Concomitantly to modification of the BChl molecule, the redox potential of the heterodimer primary donor increased relative to that of the WT organism (772 mV vs. 517 mV). The availability of this heterodimer mutant and its crystal structure provides opportunities for investigating changes in light-induced electron transfer that reflect differences in redox cascades

Ultrafast electron and hole dynamics in novel conjugated star-shaped molecules

Charge dynamics in organic photovoltaic blends based on novel star-shaped molecules are studied by ultrafast visible-IR spectroscopy. Pathways of intra- and intermolecular electron and hole transfer and their recombination are identified and discussed

Ultrafast electron and hole dynamics in novel conjugated star-shaped molecules

Charge dynamics in organic photovoltaic blends based on novel starshaped molecules are studied by ultrafast visible-IR spectroscopy. Pathways of intra-and intermolecular electron and hole transfer and their recombination are identified and discussed

Bidirectional Photoinduced Electron Transfer in Ruthenium(II)-Tris-bipyridyl-Modified PpcA, a Multi-heme <i>c</i>‑Type Cytochrome from <i>Geobacter sulfurreducens</i>

PpcA, a tri-heme cytochrome <i>c</i>₇ from <i>Geobacter sulfurreducens</i>, was investigated as a model for photosensitizer-initiated electron transfer within a multi-heme “molecular wire” protein architecture. <i>Escherichia coli</i> expression of PpcA was found to be tolerant of cysteine site-directed mutagenesis, demonstrated by the successful expression of natively folded proteins bearing cysteine mutations at a series of sites selected to vary characteristically with respect to the three -CXXCH- heme binding domains. The introduced cysteines readily reacted with Ru­(II)-(2,2′-bpy)₂(4-bromomethyl-4′-methyl-2,2′-bipyridine) to form covalently linked constructs that support both photo-oxidative and photo-reductive quenching of the photosensitizer excited state, depending upon the initial heme redox state. Excited-state electron-transfer times were found to vary from 6 × 10^–12 to 4 × 10^–8 s, correlated with the distance and pathways for electron transfer. The fastest rate is more than 10³-fold faster than previously reported for photosensitizer–redox protein constructs using amino acid residue linking. Clear evidence for inter-heme electron transfer within the multi-heme protein is not detected within the lifetimes of the charge-separated states. These results demonstrate an opportunity to develop multi-heme <i>c</i>-cytochromes for investigation of electron transfer in protein “molecular wires” and to serve as frameworks for metalloprotein designs that support multiple-electron-transfer redox chemistry

Global evolution and phylogeography of Brucella melitensis strains

Abstract Background Brucellosis is a bacterial zoonotic disease. Annually in the world more than 500,000 new cases of brucellosis in humans are registered. In this study, we propose an evolutionary model of the historical distribution of B. melitensis based on the full-genomic SNP analysis of 98 strains. Results We performed an analysis of the SNP of the complete genomes of 98 B. melitensis strains isolated in different geographical regions of the world to obtain relevant information on the population structure, genetic diversity and the evolution history of the species. Using genomic sequences of 21 strains of B. melitensis isolated in Russia and WGS data from the NCBI database, it was possible to identify five main genotypes and 13 species genotypes for analysis. Data analysis based on the Bayesian Phylogenetics and Phylogeography method allowed to determine the regions of geographical origin and the expected pathways of distribution of the main lines (genotypes and subgenotypes) of the pathogen. Conclusions Within the framework of our study, the model of global evolution and phylogeography of B. melitensis strains isolated in various regions of the planet was proposed for the first time. The sets of unique specific SNPs described in our study, for all identified genotypes and subgenotypes, can be used to develop new bacterial typing and identification systems for B. melitensis

Mimicking Natural Photosynthesis: Designing Ultrafast Photosensitized Electron Transfer into Multiheme Cytochrome Protein Nanowires

Efficient nanomaterials for artificial photosynthesis require fast and robust unidirectional electron transfer (ET) from photosensitizers through charge-separation and accumulation units to redox-active catalytic sites. We explored the ultrafast time-scale limits of photo-induced charge transfer between a Ru(II)tris(bipyridine) derivative photosensitizer and PpcA, a 3-heme c-type cytochrome serving as a nanoscale biological wire. Four covalent attachment sites (K28C, K29C, K52C, and G53C) were engineered in PpcA enabling site-specific covalent labeling with expected donor-acceptor (DA) distances of 4&ndash;8 &Aring;. X-ray scattering results demonstrated that mutations and chemical labeling did not disrupt the structure of the proteins. Time-resolved spectroscopy revealed three orders of magnitude difference in charge transfer rates for the systems with otherwise similar DA distances and the same number of covalent bonds separating donors and acceptors. All-atom molecular dynamics simulations provided additional insight into the structure-function requirements for ultrafast charge transfer and the requirement of van der Waals contact between aromatic atoms of photosensitizers and hemes in order to observe sub-nanosecond ET. This work demonstrates opportunities to utilize multi-heme c-cytochromes as frameworks for designing ultrafast light-driven ET into charge-accumulating biohybrid model systems, and ultimately for mimicking the photosynthetic paradigm of efficiently coupling ultrafast, light-driven electron transfer chemistry to multi-step catalysis within small, experimentally versatile photosynthetic biohybrid assemblies