Ubiquitin-Dependent and Independent Proteasomal Degradation in Host-Pathogen Interactions

Ubiquitin, a small protein, is well known for tagging target proteins through a cascade of enzymatic reactions that lead to protein degradation. The ubiquitin tag, apart from its signaling role, is paramount in destabilizing the modified protein. Here, we explore the complex role of ubiquitin-mediated protein destabilization in the intricate proteolysis process by the 26S proteasome. In addition, the significance of the so-called ubiquitin-independent pathway and the role of the 20S proteasome are considered. Next, we discuss the ubiquitin–proteasome system’s interplay with pathogenic microorganisms and how the microorganisms manipulate this system to establish infection by a range of elaborate pathways to evade or counteract host responses. Finally, we focus on the mechanisms that rely either on (i) hijacking the host and on delivering pathogenic E3 ligases and deubiquitinases that promote the degradation of host proteins, or (ii) counteracting host responses through the stabilization of pathogenic effector proteins

Terahertz Response of a Point Contact Based on CdTe/CdMgTe Quantum Well in Magnetic Field

A photoresponse at THz frequencies of a quantum point contact fabricated on a CdTe/CdMgTe quantum well was studied at low temperatures as a function of magnetic field. The spectra show a structure which was interpreted as resulting from the cyclotron resonance and magnetoplasmon excitations. The wavelength of the fundamental magnetoplasmon mode was found to be about 2 mu m which coincides with one of dimensions of the point contact. We also discuss the possibility of coupling of magnetoplasmon modes to shallow impurity transitions in the quantum well

Field effect transistors for terahertz imaging

International audienceResonant frequencies of the two-dimensional plasma in field effect transistors (FETs) increase with the reduction of the channel dimensions and can reach the terahertz (THz) range for micrometer and sub-micrometer channel lengths. Non linearity of the gated electron gas in the transistor channel can be used for the detection of THz radiation. The possibility of tuneable narrow band detection in sub-THz and THz range, related to plasma resonances, has been demonstrated for nanometre gate length transistors at cryogenic temperatures. At room temperatures the plasma oscillations are usually strongly damped, but field effect transistors can still operate as an efficient broadband detectors in the THz range. We present an overview of experimental results on THz detection by field effect transistors made of III-V and Si materials, The material issue is discussed and first room applications of FETs for imaging at frequencies above 1 THz are demonstrated

Anchoring a Plant Cytochrome P450 via PsaM to the Thylakoids in <i>Synechococcus</i> sp. PCC 7002: Evidence for Light-Driven Biosynthesis

<div><p>Plants produce an immense variety of specialized metabolites, many of which are of high value as their bioactive properties make them useful as for instance pharmaceuticals. The compounds are often produced at low levels in the plant, and due to their complex structures, chemical synthesis may not be feasible. Here, we take advantage of the reducing equivalents generated in photosynthesis in developing an approach for producing plant bioactive natural compounds in a photosynthetic microorganism by functionally coupling a biosynthetic enzyme to photosystem I. This enables driving of the enzymatic reactions with electrons extracted from the photosynthetic electron transport chain. As a proof of concept, we have genetically fused the soluble catalytic domain of the cytochrome P450 CYP79A1, originating from the endoplasmic reticulum membranes of <i>Sorghum bicolor</i>, to a photosystem I subunit in the cyanobacterium <i>Synechococcus</i> sp. PCC 7002, thereby targeting it to the thylakoids. The engineered enzyme showed light-driven activity both <i>in vivo</i> and <i>in vitro</i>, demonstrating the possibility to achieve light-driven biosynthesis of high-value plant specialized metabolites in cyanobacteria.</p></div

Identification of the elusive pyruvate reductase of Chlamydomonas reinhardtii chloroplasts

Under anoxic conditions the green alga Chlamydomonas reinhardtii activates various fermentation pathways leading to the creation of formate, acetate, ethanol and small amounts of other metabolites including d-lactate and hydrogen. Progress has been made in identifying the enzymes involved in these pathways and their subcellular locations; however, the identity of the enzyme involved in reducing pyruvate to d-lactate has remained unclear. Based on sequence comparisons, enzyme activity measurements, X-ray crystallography, biochemical fractionation and analysis of knock-down mutants, we conclude that pyruvate reduction in the chloroplast is catalyzed by a tetrameric NAD(+)-dependent d-lactate dehydrogenase encoded by Cre07.g324550. Its expression during aerobic growth supports a possible function as a ‘lactate valve’ for the export of lactate to the mitochondrion for oxidation by cytochrome-dependent d-lactate dehydrogenases and by glycolate dehydrogenase. We also present a revised spatial model of fermentation based on our immunochemical detection of the likely pyruvate decarboxylase, PDC3, in the cytoplasm

Verification of product formation in living cells.

<p>A) Extracted ion chromatograms (<i>m/z</i> 152) from the LC-MS analysis of metabolites extracted from the growth medium of <i>Synechococcus</i> sp. PCC 7002 WT and PsaM-CYP79A1 cultures for detection of <i>in vivo</i> activity of the PsaM-CYP79A1 complex, compared to a <i>p</i>-hydroxyphenylacetaldoxime standard (C+). The two peaks are the E and Z isomers of the <i>p</i>-hydroxyphenylacetaldoxime. B) LC-MS extracted ion chromatograms as in A, from analysis of extracts of PsaM-CYP79A1 cyanobacteria or growth medium.</p

Localization of PsaM in PSI and schematic drawing of the thylakoid in the engineered strain.

<p>A) and B) The crystal structure of a monomer of photosystem I from the cyanobacterium <i>Thermosynechococcus elongatus</i> seen from the cytoplasmic side of the thylakoid membrane (A) and from the trimer-facing side of the monomer (B). RCSB Protein Data Bank ID: 1JB0. The PsaM subunit is shown in green in both panels and additionally indicated by an arrow in panel A. C) Schematic representation of the PsaM-CYP79A1 fusion protein in the thylakoid membrane.</p

Sequences of oligonucleotide primers used in this study.

<p>Restriction sites inserted into the PCR product through the primers are underlined.</p

Localization of the PsaM-CYP79A1 fusion protein in the thylakoids.

<p>A) Immunoblot of proteins from 80 µL of the 0.5 mL fractions collected from the PsaM-CYP79A1 sucrose gradient shown in panel B), concentrated through acetone precipitation. Antibodies against the PSI subunit PsaC (∼9 kDa), the PSII subunit PsbA (∼32 kDa) and the CYP79A1 (∼61 kDa) have been used. CYP79A1, d.e.: digitally enhanced representation of the chemiluminescence signal detected from the CYP79A1 bands (shown below). C+: CYP79A1 expressed in chloroplasts of tobacco. Fraction 1 is the bottommost and fraction 28 the topmost fraction in the gradient. B) Sucrose gradients separating the components of WT and PsaM-CYP79A1 thylakoids solubilized in 1% (w/v) β-DM. C) Separation of protein complexes of β-DM-solubilized WT and PsaM-CYP79A1 thylakoids by BN-PAGE.</p