Modeling pigment contributions to spectral reflection of apple fruit.

A simple approach for spectral reconstruction of spectral reflection by whole apple fruit is described. It is shown that an approximation to the reflection spectrum can be obtained by making a simple assumption on the shape of the featureless scattering and using known spectral properties of the following pigment pools: (i) thylakoid-bound chlorophylls and carotenoids, (ii) cuticular/vacuolar phenolics, (iii) extrathylakoid chloroplasts/chromoplasts carotenoids, and (iv) vacuolar anthocyanins. The in vivo spectra of individual pigment pools estimated in bleaching experiments or as a difference between fruit with high and low pigment content are presented. In most cases simulations based on a linear combination of spectra proved to be effective, but fruit with high chlorophyll content necessitated the use of a non-linear model. The models succeeded in simulating reflection spectra of fruit widely differing in pigment content and composition with relative error lower than +/-4% over the visible range. The estimated relative contributions by the pigment pools into total reflection were found to be sensitive indicators of apple fruit ripening and could be useful in evaluating the light screening efficacy by flavonoids and carotenoids under stress conditions.     

Phage as templates for hybrid materials and mediators for nanomaterial synthesis

Genetic engineering of phage provides unprecedented opportunities to build novel nanomaterials by integrating biology, chemistry and materials science principles. By mimicking the evolution process in nature, the phage is used as an information-mining tool to identify specific peptide information that can recognize desired materials at the molecular level. The unique recognition peptides of the phage can direct peptide-mediated mineralization processes to grow many useful nanometer-scale electronic and medical materials. The monodispersity and long rod shape of the phage, bearing specific recognition motifs, enable the organization of various nanomaterials into periodically ordered hierarchical structures that could be useful for electronic, optical and biotechnological applications.     

Structural basis for the fast maturation of Arthropoda green fluorescent protein

Since the cloning of Aequorea victoria green fluorescent protein (GFP) in 1992, a family of known GFP-like proteins has been growing rapidly. Today, it includes more than a hundred proteins with different spectral characteristics cloned from Cnidaria species. For some of these proteins, crystal structures have been solved, showing diversity in chromophore modifications and conformational states. However, we are still far from a complete understanding of the origin, functions and evolution of the GFP family. Novel proteins of the family were recently cloned from evolutionarily distant marine Copepoda species, phylum Arthropoda, demonstrating an extremely rapid generation of fluorescent signal. Here, we have generated a non-aggregating mutant of Copepoda fluorescent protein and solved its high-resolution crystal structure. It was found that the protein beta-barrel contains a pore, leading to the chromophore. Using site-directed mutagenesis, we showed that this feature is critical for the fast maturation of the chromophore.     

Response of the Photosynthetic Apparatus of the Diatom Thallassiosira weisflogii to High Irradiance Light

The response of the photosynthetic apparatus to high irradiance illumination (440–2200 W/m²) was studied in the diatom Thallassiosira weisflogii by fluorescence methods. Changes in the photosynthetic apparatus were monitored by measuring characteristics of chlorophyll fluorescence F ₀, F _m, F _v/F _m, and qN for several hours after illumination of the alga with high-intensity light. Incubation of the alga with 2 mM DTT, an inhibitor of de-epoxidase of carotenoids in the diadinoxanthin cycle, led to a decrease in the nonphotochemical quenching of chlorophyll fluorescence and a drop in the F _v/F _m ratio, a characteristic that reflects the quantum efficiency of the functioning of the photosynthetic apparatus. Light-induced absorption changes associated with transformations of carotenoids of diadinoxanthin cycle were recorded in vivo in algal suspensions in the absence and in the presence of DTT. Using the microfluorometric method, we measured cell distribution over the efficiency of the primary processes of photosynthesis (F _v/F _m) after illumination. We found cells with a high tolerance of their photosynthetic apparatus to photooxidative damage. The relatively high tolerance of a portion of the cell population to high-light illumination can be related to light-induced transformation of carotenoids and to the functioning of other protective systems of the photosynthetic apparatus in diatoms.     

Differential regulation of pituitary gonadotropin subunit messenger ribonucleic acid levels in photostimulated Siberian hamsters

FSH levels begin to rise 3-5 days after male Siberian hamsters are transferred from inhibitory short photoperiods to stimulatory long photoperiods. In contrast, LH levels do not increase for several weeks. This differential pattern of FSH and LH secretion represents one of the most profound in vivo examples of differential regulation of the gonadotropins. The present study was undertaken to characterize the molecular mechanisms controlling differential FSH and LH synthesis and secretion in photostimulated Siberian hamsters. First, we cloned species-specific cDNAs for the three gonadotropin subunits: the common alpha subunit and the unique FSHbeta and LHbeta subunits. All three subunits share high nucleotide and predicted amino acid sequence identity with the orthologous cDNAs from rats. We then used these new molecular probes to examine the gonadotropin subunit mRNA levels from pituitaries of short-day male hamsters transferred to long days for 2, 5, 7, 10, 15, or 20 days. Short-day (SD) and long-day (LD) controls remained in short and long days, respectively, from the time of weaning. We measured serum FSH and LH levels by RIA. FSHbeta, LHbeta, and alpha subunit mRNA levels were measured from individual pituitaries using a microlysate ribonuclease protection assay. Serum FSH and pituitary FSHbeta mRNA levels changed similarly following long-day transfer. Both were significantly elevated after five long days (2.3- and 3.6-fold, respectively; P < 0.02) and declined thereafter, but they remained above SD control values through 20 long days. Alpha subunit mRNA levels also increased significantly relative to SD control values (maximum 2-fold increase after seven long days; P < 0.03), although to a lesser extent than FSHbeta. Neither serum LH nor pituitary LHbeta mRNA levels changed significantly following long-day transfer. The results indicate that long-day-associated increases in serum FSH levels in Siberian hamsters reflect an underlying increase in pituitary FSHbeta and alpha subunit mRNA accumulation.     

Electrophysiological evidence for heptameric stoichiometry of ion channels formed by Staphylococcus aureus alpha-toxin in planar lipid bilayers

Staphylococcal alpha-toxin forms homo-oligomeric channels in lipid bilayers and cell membranes. Here, we report that electrophysiological monitoring of single-channel function using a derivatized cysteine substitution mutant allows accurate determination of the subunit stoichiometry of the oligomer in situ. The electrophysiological phenotype of channels formed in planar lipid bilayers with the cysteine replacement mutant I7C is equal to that of the wild type. When pores were formed with I7C, alterations of several channel properties were observed upon modification with SH reagents. Decreases in conductance then occurred that were seen only as negative voltage was applied. At the level of single channels, these were manifest as stepwise changes in conductance, each step most probably reflecting modification of a single SH group within the oligomer. Because seven steps were observed, the functional channel formed by alpha-toxin in planar lipid membranes is a heptamer.     

Protein electrostriction: a possibility of elastic deformation of the α-hemolysin channel by the applied field

While conformational flexibility of proteins is widely recognized as one of their functionally crucial features and enjoys proper attention for this reason, their elastic properties are rarely discussed. In ion channel studies, where the voltage-induced or ligand-induced conformational transitions, gating, are the leading topic of research, the elastic structural deformation by the applied electric field has never been addressed at all. Here we examine elasticity using a model channel of known crystal structure—Staphylococcus aureus -hemolysin. Working with single channels reconstituted into planar lipid bilayers, we first show that their ionic conductance is asymmetric with voltage even at the highest salt concentration used where the static charges in the channel interior are maximally shielded. Second, choosing 18-crown-6 as a molecular probe whose size is close to the size of the narrowest part of the -hemolysin pore, we analyze the blockage of the channel by the crown/K⁺ complex. Analysis of the blockage within the framework of the Woodhull model in its generalized form demonstrates that the model is able to correctly describe the crown effect only if the parameters of the model are considered to be voltage-dependent. Specifically, one has to include either a voltage-dependent barrier for crown release to the cis side of the channel or voltage-dependent interactions between the binding site and the crown. We suggest that the voltage sensitivity of both the ionic conductance of the channel seen at the highest salt concentration and its blockage by the crown reflects a field-induced deformation of the pore.     

Screening of visible and UV radiation as a photoprotective mechanism in plants

Prolonged exposure of plants to high fluxes of solar radiation as well as to other environmental stressors disturbs the balance between absorbed light energy and capacity of its photochemical utilization resulting in photoinhibition of and eventually in damage to plants. Under such circumstances, the limiting of the light absorption by the photosynthetic apparatus efficiently augments the general photoprotective mechanisms of the plant cell, such as reparation of macromolecules, elimination of reactive oxygen species, and thermal dissipation of the excessive light energy absorbed. Under stressful conditions, plants accumulate, in different cell compartments and tissue structures, pigments capable of attenuation of the radiation in the UV and visible parts of the spectrum. To the date, four principle key groups of photoprotective pigments are known: mycosporine-like amino acids, phenolic compounds (including phenolic acids, flavonols, and anthocyanins), alkaloids (betalains), and carotenoids. The accumulation of UV-absorbing compounds (mycosporine-like amino acids and phenolics in lower and higher plants, respectively) is a ubiquitous mechanism of adaptation to and protection from the damage by high fluxes of solar radiation developed by photoautotrophic organisms at the early stages of their evolution. Extrathylakoid carotenoids, betalains, and anthocyanins play an important role in long-term adaptation to the illumination conditions and in protection of plants against photodamage. A prominent feature of certain plant taxa lacking some classes of photoprotective pigments (such as anthocyanins) is their substitution by other compounds (e.g. keto-carotenoids or betalains) disparate in terms of chemical structure and subcellular localization but possessing close spectral properties.