Conformational relaxation following reduction of the photoactive bacteriopheophytin in reaction centers from Blastochloris viridis. Influence of mutations at position M208

AbstractThe photochemically trapped bacteriopheophytin (BPh) b radical anion in the active branch (ΦA−) of reaction centers (RCs) from Blastochloris (formerly called Rhodopseudomonas) viridis is characterized by 1H-ENDOR as well as optical absorption spectroscopy. The two site-directed mutants YF(M208) and YL(M208), in which tyrosine at position M208 is replaced by phenylalanine and leucine, respectively, are investigated and compared with the wild type. The residue at M208 is in close proximity to the primary electron donor, P, the monomeric bacteriochlorophyll (BChl), BA, and the BPh, ΦA, that are involved in the transmembrane electron transfer to the quinone, QA, in the RC. The analysis of the ENDOR spectra of ΦA− at 160 K indicates that two distinct states of ΦA− are present in the wild type and the mutant YF(M208). Based on a comparison with ΦA− in RCs of Rhodobacter sphaeroides the two states are interpreted as torsional isomers of the 3-acetyl group of ΦA. Only one ΦA− state occurs in the mutant YL(M208). This effect of the leucine residue at position M208 is explained by steric hindrance that locks the acetyl group in one specific position. On the basis of these results, an interpretation of the optical absorption difference spectrum of the state ΦA−QA− is attempted. This state can be accumulated at 100 K and undergoes an irreversible change between 100 and 200 K [Tiede et al., Biochim. Biophys. Acta 892 (1987) 294–302]. The corresponding absorbance changes in the BChl Qx and Qy regions observed in the wild type also occur in the YF(M208) mutant but not in YL(M208). The observed changes in the wild type and YF(M208) are assigned to RCs in which the 3-acetyl group of ΦA changes its orientation. It is concluded that this distinct structural relaxation of ΦA can significantly affect the optical properties of BA and contribute to the light-induced absorption difference spectra

Fluorescence microscopy visualization of halomucin, a secreted 927 kDa protein surrounding Haloquadratum walsbyi cells

At the time of its first publication, halomucin from Haloquadratum walsbyi strain HBSQ001 was the largest archaeal protein known (9159 aa). It has a predicted signal sequence, making it likely to be an extracellular or secreted protein. Best BLAST matches were found to be mammalian mucins that protect tissues to dehydration and chemical stress. It was hypothesized that halomucin participates in protection against desiccation by retaining water in a hull around the halophilic organisms that live at the limits of water activity. We visualized Halo quadratum cells by staining their intracellular polyhydroxybutyrate granules using Nile Blue. Halomucin was stained by immunofluorescence with antibodies generated against synthetic peptides derived from the halomucin amino acid sequence. Polyhydroxybutyrate stained cells were reconstructed in 3D which highlights not only the highly regular square shape but also the extreme flatness of Haloquadratum. Double-staining proves halomucin to be extracellular but to be only loosely associated to cells in agreement with its hypothesized function

Systems analysis of bioenergetics and growth of the extreme halophile Halobacterium salinarum

Halobacterium salinarum is a bioenergetically flexible, halophilic microorganism that can generate energy by respiration, photosynthesis, and the fermentation of arginine. In a previous study, using a genome-scale metabolic model, we have shown that the archaeon unexpectedly degrades essential amino acids under aerobic conditions, a behavior that can lead to the termination of growth earlier than necessary. Here, we further integratively investigate energy generation, nutrient utilization, and biomass production using an extended methodology that accounts for dynamically changing transport patterns, including those that arise from interactions among the supplied metabolites. Moreover, we widen the scope of our analysis to include phototrophic conditions to explore the interplay between different bioenergetic modes. Surprisingly, we found that cells also degrade essential amino acids even during phototropy, when energy should already be abundant. We also found that under both conditions considerable amounts of nutrients that were taken up were neither incorporated into the biomass nor used as respiratory substrates, implying the considerable production and accumulation of several metabolites in the medium. Some of these are likely the products of forms of overflow metabolism. In addition, our results also show that arginine fermentation, contrary to what is typically assumed, occurs simultaneously with respiration and photosynthesis and can contribute energy in levels that are comparable to the primary bioenergetic modes, if not more. These findings portray a picture that the organism takes an approach toward growth that favors the here and now, even at the cost of longer-term concerns. We believe that the seemingly "greedy" behavior exhibited actually consists of adaptations by the organism to its natural environments, where nutrients are not only irregularly available but may altogether be absent for extended periods that may span several years. Such a setting probably predisposed the cells to grow as much as possible when the conditions become favorable

Antecedentes de las consultas de boca-oído online sobre hoteles

Las consultas online sobre productos y servicios antes de la compra han recibido menor atención en la literatura que la generación de comentarios después de la experiencia. Nuestro trabajo aborda, por tanto, el estudio de la conducta de boca-oído online desde la perspectiva del receptor. El objetivo es investigar las variables que contribuyen en la adopción de boca-oído online para tomar la decisión de elección de un hotel. Para ello, se analiza la cadena de relaciones “motivaciones→intención de consultar→volumen→adopción”, considerando tres tipos de motivaciones: conveniencia, riesgo y sociales. Con una muestra de 393 huéspedes de hoteles de 3, 4 y 5 estrellas y a partir de un modelo de ecuaciones estructurales, los resultados confirman las relaciones, siendo las motivaciones de conveniencia y riesgo las únicas que influyen en la intención de consultar boca-oído online. Se presentan implicaciones académicas para avanzar en este campo de estudio y recomendaciones para la gestión empresarial.Online reviews about goods and services prior to purchase have received less attention in the literature than comments generation after the experience. Our work addresses the study of online word-of-mouth behaviour from the receiver perspective. The aim is to investigate the variables that contribute to word-of-mouth adoption in order to make the decision to choose a hotel. The relationships chain “motivations→consult intention→volume→adoption” is analyzed, considering three types of motivations: convenience, risk and social. With a sample of 393 guests from 3, 4 and 5 star hotels and by means of a structural equations model, the results confirm these relationships, and the motivations of convenience and risk are the only ones that influence the intention to consult online word-of-mouth. Academic implications and recommendations for business management are presented to advance in this field of study

Structure of the archaeal chemotaxis protein CheY in a domain-swapped dimeric conformation

Archaea are motile by the rotation of the archaellum. The archaellum switches between clockwise and counterclockwise rotation, and movement along a chemical gradient is possible by modulation of the switching frequency. This modulation involves the response regulator CheY and the archaellum adaptor protein CheF. In this study, two new crystal forms and protein structures of CheY are reported. In both crystal forms, CheY is arranged in a domain-swapped conformation. CheF, the protein bridging the chemotaxis signal transduction system and the motility apparatus, was recombinantly expressed, purified and subjected to X-ray data collection