Identification of a human HLA-E-restricted CD8+ T cell subset in volunteers immunized with Salmonella enterica serovar Typhi strain Ty21a typhoid vaccine

Our previous studies in volunteers immunized with Salmonella enterica serovar Typhi (S. Typhi) have suggested an important role for CD8+ T cells in host defense. In this study we describe a novel subset of nonclassical human HLA-E-restricted S. Typhi-specific CD8+ T cells derived from PBMC of Ty21a typhoid vaccinees. CD3+CD8+CD4-CD56- T cells effectively killed S. Typhi-infected targets regardless of whether they share classical HLA class I molecules with them, by a FAS-independent, granule-dependent mechanism, as evidenced by induction of granzyme B release and the blocking effects of concanamycin and strontium ions. The expression of HLA-E Ags, but not CD1-a, -b, or -c, on the membrane of S. Typhi-infected targets rendered them susceptible to lysis. Moreover, anti-HLA-E Abs partially blocked these responses. We also demonstrated that presentation of S. Typhi Ags via HLA-E could stimulate IFN-gamma production. Increases in the net frequency of IFN-gamma spot-forming cells were observed in the presence of targets coated with peptides that contain S. Typhi GroEL HLA-E binding motifs. These results demonstrate that HLA-E binds nonamer peptides derived from bacterial proteins and trigger CD8+-mediated lysis and IFN-gamma production when exposed to infected targets, raising the possibility that this novel effector mechanism might contribute to host defense against intracellular bacterial infections.     

Biosynthesis of amphetamine analogs in plants

Amphetamine analogs are produced by plants in the genus Ephedra and by Catha edulis, and include the widely used decongestants and appetite suppressants pseudoephedrine and ephedrine. A combination of yeast (Candida utilis or Saccharomyces cerevisiae) fermentation and subsequent chemical modification is used for the commercial production of these compounds. The availability of certain plant biosynthetic genes would facilitate the engineering of yeast strains capable of de novo pseudoephedrine and ephedrine biosynthesis. Chemical synthesis has yielded amphetamine analogs with myriad functional group substitutions and diverse pharmacological properties. The isolation of enzymes with the serendipitous capacity to accept novel substrates could allow the production of substituted amphetamines in synthetic biosystems. Here, we review the biology, biochemistry and biotechnological potential of amphetamine analogs in plants.     

Constrained analysis of fluorescence anisotropy decay:application to experimental protein dynamics

Hydrodynamic properties as well as structural dynamics of proteins can be investigated by the well-established experimental method of fluorescence anisotropy decay. Successful use of this method depends on determination of the correct kinetic model, the extent of cross-correlation between parameters in the fitting function, and differences between the timescales of the depolarizing motions and the fluorophore's fluorescence lifetime. We have tested the utility of an independently measured steady-state anisotropy value as a constraint during data analysis to reduce parameter cross correlation and to increase the timescales over which anisotropy decay parameters can be recovered accurately for two calcium-binding proteins. Mutant rat F102W parvalbumin was used as a model system because its single tryptophan residue exhibits monoexponential fluorescence intensity and anisotropy decay kinetics. Cod parvalbumin, a protein with a single tryptophan residue that exhibits multiexponential fluorescence decay kinetics, was also examined as a more complex model. Anisotropy decays were measured for both proteins as a function of solution viscosity to vary hydrodynamic parameters. The use of the steady-state anisotropy as a constraint significantly improved the precision and accuracy of recovered parameters for both proteins, particularly for viscosities at which the protein's rotational correlation time was much longer than the fluorescence lifetime. Thus, basic hydrodynamic properties of larger biomolecules can now be determined with more precision and accuracy by fluorescence anisotropy decay.     

Antigenic cross-reactivity among monoterpene cyclases from grand fir and induction of these enzymes upon stem wounding.

A major wound response in grand fir (Abies grandis) sapling stems is the rapid increase in monoterpene production at the site of injury. Monoterpene cyclases (synthases) catalyze the formation of monoterpenes from geranyl pyrophosphate, and total cyclase activity increases markedly on wounding. At least six distinct cyclases, producing different monoterpene products, have been isolated from wounded grand fir saplings and characterized. The predominant wound-inducible cyclase produces both alpha- and beta-pinene. This pinene cyclase was purified, and polyclonal antibodies were generated in rabbits against the sodium dodecyl sulfate-denatured protein. The antibody preparation was found to cross-react by Western blotting with other grand fir monoterpene cyclases that produce different olefinic products, but not with monoterpene cyclases from related conifer species (Pinus contorta and P. ponderosa) or from angiosperms (Mentha piperita and M. spicata). The increase in monoterpene cyclase activity after wounding was closely correlated with the appearance of new cyclase protein as determined by immunoblotting. These results indicate that the wound-dependent increase in monoterpene cyclase activity is a consequence of de novo synthesis of cyclase protein.     

Citrus fruit bitter flavors: isolation and functional characterization of the gene Cm1,2RhaT encoding a 1,2 rhamnosyltransferase, a key enzyme in the biosynthesis of the bitter flavonoids of citrus

Species of the genus Citrus accumulate large quantities of flavanones that affect fruit flavor and have been documented to benefit human health. Bitter species, such as grapefruit and pummelo, accumulate bitter flavanone-7-O-neohesperidosides responsible, in part, for their characteristic taste. Non-bitter species, such as mandarin and orange, accumulate only tasteless flavanone-7-O-rutinosides. The key flavor-determining step of citrus flavanone-glycoside biosynthesis is catalyzed by rhamnosyltransferases; 1,2 rhamnosyltransferases (1,2RhaT) catalyze biosynthesis of the bitter neohesperidosides, while 1,6 rhamnosyltransferases (1,6RhaT) catalyze biosynthesis of the tasteless rutinosides. We report on the isolation and functional characterization of the gene Cm1,2RhaT from pummelo which encodes a citrus 1,2RhaT. Functional analysis of Cm1,2RhaT recombinant enzyme was conducted by biotransformation of the substrates using transgenic plant cell culture. Flavanones and flavones, but not flavonols, were biotransformed into 7-O-neohesperidosides by the transgenic BY2 tobacco cells expressing recombinant Cm1,2RhaT. Immunoblot analysis established that 1,2RhaT protein was expressed only in the bitter citrus species and that 1,6RhaT enzyme, whose activity was previously documented in non-bitter species, was not cross-reactive. Expression of Cm1,2RhaT at the RNA level was prominent in young fruit and leaves, but low in the corresponding mature tissue, thus correlating well with the developmental pattern of accumulation of flavanone-neohesperidosides previously established. Phylogenetic analysis of the flavonoid glycosyltransferase gene family places Cm1,2RhaT on a separate gene cluster together with the only other functionally characterized flavonoid-glucoside rhamnosyltransferase gene, suggesting a common evolutionary origin for rhamnosyltransferases specializing in glycosylation of the sugar moieties of flavonoid glucosides.     

Stimulation of adenine nucleotide translocation in reconstituted vesicles by phosphate and the phosphate transporter

Highly purified adenine nucleotide transporter from bovine heart mitochondria was reconstituted with phospholipids to form vesicles which catalyzed atractyloside-sensitive adenine nucleotide translocation. When internal ATP was exchanged with external ADP, this reaction was enhanced by agents capable of collapsing a membrane potential, but not by inorganic phosphate. When the purified nucleotide transporter was reconstituted together with a second protein fraction, nucleotide transport was stimulated by inorganic phosphate. The stimulated rate was eliminated by mersalyl or other SH reagents. The second protein fraction could be replaced by preparations of purified phosphate transporter.     

Diversity of common beans (Phaseolus vulgaris,Fabaceae) and conditions of production in Aguascalientes,Mexico

This study analyzes the regional diversity of common beans (Phaseolus vulgaris, Fabaceae) in Aguascalientes, Mexico, in relation to local physical, biological, cultural, and socioeconomic factors. A close direct relationship between bean diversity and the physical and biological factors and a close inverse relationship between bean diversity and the cultural and socioeconomic factors was found. Greater bean diversity was found in areas under rainfed conditions with low-input traditional agriculture where farmers with low income cultivate a great number of local heterogeneous landraces to insure some production for home use in spite of environmental stress conditions. Reduced bean diversity is cultivated under irrigated conditions with high-input modern agriculture where farmers with high income grow a few uniform improved cultivars to obtain high yields for commercial purposes. A previous study showed greater morphological variation in the seed collected in the 1940s compared to that collected in 1984. The bean variants of 1984 showed significantly earlier maturation. These findings suggest the necessity of periodic studies for a better understanding of the dynamic process of evolution of beans under continuous ecological, cultural, and socioeconomic change.     

An integrated framework to improve the concept of resource specialisation

Resource specialisation, although a fundamental component of ecological theory, is employed in disparate ways. Most definitions derive from simple counts of resource species. We build on recent advances in ecophylogenetics and null model analysis to propose a concept of specialisation that comprises affinities among resources as well as their co‐occurrence with consumers. In the distance‐based specialisation index (DSI), specialisation is measured as relatedness (phylogenetic or otherwise) of resources, scaled by the null expectation of random use of locally available resources. Thus, specialists use significantly clustered sets of resources, whereas generalists use over‐dispersed resources. Intermediate species are classed as indiscriminate consumers. The effectiveness of this approach was assessed with differentially restricted null models, applied to a data set of 168 herbivorous insect species and their hosts. Incorporation of plant relatedness and relative abundance greatly improved specialisation measures compared to taxon counts or simpler null models, which overestimate the fraction of specialists, a problem compounded by insufficient sampling effort. This framework disambiguates the concept of specialisation with an explicit measure applicable to any mode of affinity among resource classes, and is also linked to ecological and evolutionary processes. This will enable a more rigorous deployment of ecological specialisation in empirical and theoretical studies.