Spectroscopic and theoretical approaches for studying radical reactions in class I ribonucleotide reductase

Ribonucleotide reductases (RNRs) catalyze the production of deoxyribonucleotides, which are essential for DNA synthesis and repair in all organisms. The three currently known classes of RNRs are postulated to utilize a similar mechanism for ribonucleotide reduction via a transient thiyl radical, but they differ in the way this radical is generated. Class I RNR, found in all eukaryotic organisms and in some eubacteria and viruses, employs a diferric iron center and a stable tyrosyl radical in a second protein subunit, R2, to drive thiyl radical generation near the substrate binding site in subunit R1. From extensive experimental and theoretical research during the last decades, a general mechanistic model for class I RNR has emerged, showing three major mechanistic steps: generation of the tyrosyl radical by the diiron center in subunit R2, radical transfer to generate the proposed thiyl radical near the substrate bound in subunit R1, and finally catalytic reduction of the bound ribonucleotide. Amino acid- or substrate-derived radicals are involved in all three major reactions. This article summarizes the present mechanistic picture of class I RNR and highlights experimental and theoretical approaches that have contributed to our current understanding of this important class of radical enzymes

Effect of selenization conditions on the growth and properties of Cu2ZnSn(S,Se)4 thin films

The opto-electronic properties of copper zinc tin sulfide can be tuned to achieve better cell efficiencies by controlled incorporation of selenium. In this paper we report the growth of Cu2ZnSn(S,Se)4 (CZTSSe) using a hybrid process involving the sequential evaporation of Zn and sputtering of the sulfide precursors of Cu and Sn, followed by a selenization step. Two approaches for selenization were followed, one using a tubular furnace and the other using a rapid thermal processor. The effects of annealing conditions on the morphological and structural properties of the films were investigated. Scanning electron microscopy and energy dispersive spectroscopy were employed to investigate the morphology and composition of the films. Structural analyses were done using X-ray diffraction (XRD) and Raman spectroscopy. Structural analyses revealed the formation of CZTSSe. This study shows that regardless of the selenization method a temperature above 450 °C is required for conversion of precursors to a compact CZTSSe layer. XRD and Raman analysis suggests that the films selenized in the tubular furnace are selenium rich whereas the samples selenized in the rapid thermal processor have higher sulfur content

Acquisition of flocculation phenotype by Kluyveromyces marxianus when overexpressing GAP1 gene encoding an isoform of glyceraldehyde-3-phosphate dehydrogenase

The use of flocculating yeast strains has been considered as a convenient approach to obtain high cell densities in bioreactors with increasing productivity in continuous operations. In Kluyveromyces marxianus ATTC 10022, the GAP1 gene encodes an isoform of glyceraldehyde-3-phosphate dehydrogenase–p37—that is accumulated in the cell wall and is involved in flocculation. To test the use of p37 as a tool for engineering Kluyveromyces cells to display a flocculation phenotype, K. marxianus CCT 3172 was transformed with an expression vector containing GAP1. This vector is based on the pY37 previously described, harbouring a S11 Kluyveromyces origin of replication, and the expression of GAP1 is under the control of GAL1. Kluyveromyces cells overexpressing GAP1 acquired a flocculent phenotype together with the accumulation of p37 in the cell wall. The results support the use of GAP1 gene as a molecular tool for inducing flocculation.Fundação para a Ciência e a Tecnologia (FCT) - BD/18203/98

Optoelectronic simulations for novel light management concepts in Cu(In,Ga)Se2 solar cells

One of the trends making its way through the Photovoltaics (PV) industry, is the search for new application possibilities. Cu(In,Ga)Se2 (CIGS) thin film solar cells stand out due to their class leading power conversion efficiency of 23.35 %, flexibility, and low cost. The use of sub-μm ultrathin CIGS solar cells has been gaining prevalence, due to the reduction in material consumption and the manufacturing time. Precise CIGS finite-difference time-domain (FDTD) and 3D-drift diffusion baseline models were developed for the Lumerical suite and a 1D electrical model for SCAPS, allowing for an accurate description of the optoelectronic behavior and response of thin and ultrathin CIGS solar cells. As a result, it was possible to obtain accurate descriptions of the optoelectronic behavior of thin and ultrathin solar cells, and to perform an optical study and optimization of novel light management approaches, such as, random texturization, photonic nanostructures, plasmonic nanoparticles, among others. The developed light management architectures enabled to push the optical performance of an ultrathin solar cell and even surpass the performance of a thin film solar cell, enabling a short-circuit current enhancement of 6.15 mA/cm2 over an ultrathin reference device, without any light management integrated.publishe

Molecular detection of HPV 16 and 18 in cervical samples of patients from Belo Horizonte, Minas Gerais, Brazil

PURPOSE: The aim of this study was to investigate the frequency of HPV infection and the types 16 and 18 in cervical samples from patients attended at two public health services of the city of Belo Horizonte, MG. METHODS: Cervical samples from 174 patients were collected for cytopathological and molecular tests. HPV infection was searched by PCR utilizing MY09 and MY11 primers or HPV 16 and HPV 18 specific primers. RESULTS: Amongst the 174 samples analyzed, 20.7% presented squamous intraepithelial and/or invasive lesions detected on cytopathological analysis and of those, 94.4% were infected by HPV. HPV 16 was found in 20% of the cases of low-grade squamous intraepithelial lesions and in 40% and 50% of high-grade squamous intraepithelial lesion and squamous invasive carcinoma, respectively. HPV 18 was detected in 6.7% of the low-grade lesion samples and in two HPV16 co-infected samples. In 50% of the cases of high-grade lesion, the HPV type was not determined. CONCLUSION: The HPV 16 was the virus type more frequently detected. However, more than 50% of the positive samples at the cytopathological analysis were negative for HPV 16 and 18, indicating that possibly other virus types are present in relative high frequencies in the studied population.OBJETIVOS: O objetivo deste estudo foi investigar a freqüência da infecção por HPV e dos tipos 16 e 18 em amostras cervicais de pacientes atendidas em dois serviços públicos da cidade de Belo Horizonte-MG. MÉTODOS: Amostras cervicais de 174 pacientes foram coletadas para estudo citopatológico e molecular. A pesquisa da infecção por HPV foi feita através da PCR utilizando os oligonucleotídeos MY09/MY11. Os tipos virais 16 e 18 foram pesquisados através da utilização de oligonucleotídeos específicos. RESULTADOS: Dentre as 174 amostras analisadas, 20,7% apresentaram lesões escamosas intra-epiteliais e/ou invasoras detectadas na análise citopatológica, das quais 94,4% mostraram infecção por HPV. O HPV 16 foi encontrado em torno de 20% dos casos de lesão escamosa intra-epitelial de baixo grau e em 40% e 50% dos casos de lesão escamosa intra-epitelial de alto grau e carcinoma escamoso invasor, respectivamente. O HPV 18 foi encontrado em 6,7% das amostras com lesão de baixo grau e em dois casos de co-infecção com HPV 16. Em 50% dos casos de lesão de alto grau, o tipo de HPV não foi determinado. CONCLUSÕES: O HPV 16 foi o tipo viral mais freqüentemente detectado. No entanto, mais de 50% das amostras positivas no exame citopatológico não apresentaram HPV 16 e 18, indicando que possivelmente outros tipos virais estejam presentes em freqüências relativamente altas na população estudada

Gathering Computational Genomics and Proteomics to Unravel Adaptive Evolution

A recent editorial in PLoS Biology by MacCallum and Hill (2006) pointed out the inappropriateness of studies evaluating signatures of positive selection based solely in single-site analyses. Therefore the rising number of articles claiming positive selection that have been recently published urges the question of how to improve the bioinformatics standards for reliably unravel positive selection? Deeper integrative efforts using state-of-the-art methodologies at the gene-level and protein-level are improving positive selection studies. Here we provide some computational guidelines to thoroughly document molecular adaptation

Non-bisphosphonate inhibitors of isoprenoid biosynthesis identified via computer-aided drug design.

The relaxed complex scheme, a virtual-screening methodology that accounts for protein receptor flexibility, was used to identify a low-micromolar, non-bisphosphonate inhibitor of farnesyl diphosphate synthase. Serendipitously, we also found that several predicted farnesyl diphosphate synthase inhibitors were low-micromolar inhibitors of undecaprenyl diphosphate synthase. These results are of interest because farnesyl diphosphate synthase inhibitors are being pursued as both anti-infective and anticancer agents, and undecaprenyl diphosphate synthase inhibitors are antibacterial drug leads

Functional and structural mimics of superoxide dismutase enzymes

Superoxide dismutase (SOD) enzymes form important defence line in living organisms. Through a dismutation reaction they transform the highly reactive superoxide radical ion to oxygen and hydrogen peroxide. The latter compound is further transformed by catalase or peroxidase enzymes to water and oxygen. The overall structure of the enzymes and those of the active sites are largely known, thus, it has been revealed that in eukaryotes Cu(II) and Zn(II) ions act as cofactors and they are connected with an imidazolate bridge and this structural unit is coordinated with amino acids. In prokaryotes the SOD enzymes contain Mn(II) or Fe(II) or Ni(II) in their active centres. In order to learn about the working mechanism of SOD enzymes at the molecular level various structural mimics were prepared and their structural transformations during the dismutation reaction was followed. Gathering adequate amount of information allowed the preparation of functional mimics that are not necessarily copies of the active sites of the enzymes, nevertheless, display considerable SOD activity. Both functional and structural mimics are comprehensively dealt with in this review. Although enzymes may seem to be attractive catalysts for promoting real-life reactions effectively with high selectivity, they can seldom if ever be used under industrial conditions, i.e. at high temperatures and pressures. The SOD enzymes for promoting oxygen transfer reactions are not durable enough under these conditions either. The complexes mimicking SOD activities perform better in this respect, however, their reusabilities are limited, because of separation problems. A solution can be the immobilisation of these SOD mimicking complexes on solid or semi-solid supports. Even if the activity is not better then the support-free complexes, the catalyst can be filtered at the end of the reaction and can easily be recycled. Attempts for immobilisation are also comprehensively reviewed and immobilised complexes with surprisingly high SOD activities are reported as well. Full characterisation of these materials is given and rationalisation of their exceptionally high activities is offered