Overexpression of phytochelatin synthase in tobacco: distinctive effects of AtPCS1 and CePCS genes on plant response to cadmium

Phytochelatins, heavy-metal-binding polypeptides, are synthesized by phytochelatin synthase (PCS) (EC 2.3.2.15). Previous studies on plants overexpressing PCS genes yielded contrasting phenotypes, ranging from enhanced cadmium tolerance and accumulation to cadmium hypersensitivity. This paper compares the effects of overexpression of AtPCS1 and CePCS in tobacco (Nicotiana tabacum var. Xanthi), and demonstrates how the introduction of single homologous genes affects to a different extent cellular metabolic pathways leading to the opposite of the desired effect. In contrast to WT and CePCS transformants, plants overexpressing AtPCS1 were Cd-hypersensitive although there was no substantial difference in cadmium accumulation between studied lines. Plants exposed to cadmium (5 and 25 μM CdCl2) differed, however, in the concentration of non-protein thiols (NPT). In addition, PCS activity in AtPCS1 transformants was around 5-fold higher than in CePCS and WT plants. AtPCS1 expressing plants displayed a dramatic accumulation of γ-glutamylcysteine and concomitant strong depletion of glutathione. By contrast, in CePCS transformants, a smaller reduction of the level of glutathione was noticed, and a less pronounced change in γ-glutamylcysteine concentration. There was only a moderate and temporary increase in phytochelatin levels due to AtPCS1 and CePCS expression. Marked changes in NPT composition due to AtPCS1 expression led to moderately decreased Cd-detoxification capacity reflected by lower SH:Cd ratios, and to higher oxidative stress (assessed by DAB staining), which possibly explains the increase in Cd-sensitivity. The results indicate that contrasting responses to cadmium of plants overexpressing PCS genes might result from species-dependent differences in the activity of phytochelatin synthase produced by the transgenes

An avian influenza H5N1 virus vaccine candidate based on the extracellular domain produced in yeast system as subviral particles protects chickens from lethal challenge

AbstractHighly pathogenic avian influenza is an on-going problem in poultry and a potential human pandemic threat. Pandemics occur suddenly and vaccine production must be fast and effective to be of value in controlling the spread of the virus. In this study we evaluated the potential of a recombinant protein from the extracellular domain of an H5 hemagglutinin protein produced in a yeast expression system to act as an effective vaccine. Protein production was efficient, with up to 200 mg purified from 1 L of culture medium. We showed that the deletion of the multibasic cleavage site from the protein improves oligomerization and, consequentially, its immunogenicity. We also showed that immunization with this deleted protein protected chickens from challenge with a highly pathogenic avian influenza H5N1 virus. Our results suggest that this recombinant protein produced in yeast may be an effective vaccine against H5N1 virus in poultry

Application of Ni(II)-Assisted Peptide Bond Hydrolysis to Non-Enzymatic Affinity Tag Removal

In this study, we demonstrate a non-enzymatic method for hydrolytic peptide bond cleavage, applied to the removal of an affinity tag from a recombinant fusion protein, SPI2-SRHWAP-His6. This method is based on a highly specific Ni(II) reaction with (S/T)XHZ peptide sequences. It can be applied for the protein attached to an affinity column or to the unbound protein in solution. We studied the effect of pH, temperature and Ni(II) concentration on the efficacy of cleavage and developed an analytical protocol, which provides active protein with a 90% yield and ∼100% purity. The method works well in the presence of non-ionic detergents, DTT and GuHCl, therefore providing a viable alternative for currently used techniques

Sequence-specific Ni(II)-dependent peptide bond hydrolysis in a peptide containing threonine and histidine residues

Previously we demonstrated that Ni(II) complexes of Ac-Thr-Glu-Ser-His-His-Lys-NH2 hexapeptide, representing residues 120-125 of human histone H2A, and some of its analogs undergo E-S peptide bond hydrolysis. In this work we demonstrate a similar coordination and reactivity pattern in Ni(II) complexes of Ac-Thr-Glu-Thr-His-His-Lys-NH2, its threonine analogue, studied using potentiometry, electronic absorption spectroscopy and HPLC. For the first time we present the detailed temperature and pH dependence of such Ni(II)-dependent hydrolysis reactions. The temperature dependence of the rate of hydrolysis yielded activation energy Ea = 92.0 kJ mol-1 and activation entropy ΔS≠ = 208 J mol-1 K-1. The pH profile of the reaction rate coincided with the formation of the four-nitrogen square-planar Ni(II) complex of Ac-Thr-Glu-Thr-His-His-Lys-NH2. These results expand the range of protein sequences susceptible to Ni(II) dependent cleavage by those containing threonine residues and permit predictions of the course of this reaction at various temperatures and pH values

The temperature dependence of the 1^st order rate constant and reaction half-times for SPI2-SRHWAP-His₆ hydrolysis in solution, at H 8.2, determined by HPLC.

<p>The temperature dependence of the 1^st order rate constant and reaction half-times for SPI2-SRHWAP-His₆ hydrolysis in solution, at H 8.2, determined by HPLC.</p

The examples of chromatograms of reaction mixture containing initially 80 µM SPI2-SRHWAP-His₆ fusion protein loaded on the Ni-NTA-agarose column, incubated with 4 mM NiCl₂ in 100 mM Hepes buffer, pH 8.2 at 50°C.

<p>From top to bottom: control fusion protein (incubated without Ni(II) ions), incubation buffer, and two pooled wash fractions (250 mM imidazole) after 22 h of incubation.</p

Arrhenius plots, demonstrating the temperature dependence of hydrolysis reaction rates at pH 8.2 for SPI2-SRHWAP-His₆ fusion protein hydrolysed in-solution (black), and on-column (blue), compared to that of the Ac-GASRHWKFL-amide peptide (red)

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0036350#pone.0036350-Kopera1" target="_blank">[<b>17</b>]</a><b>.</b> Lines represent linear fits to experimental points.</p

Alternative approaches to Ni(II)-dependent affinity tag cleavage in protein purification.

<p>The tag can be removed in solution (left) or when immobilized at the affinity column (right).</p