Chemical flexibility of heterobimetallic Mn/Fe cofactors : R2lox and R2c proteins

A heterobimetallic Mn/Fe cofactor is present in the R2 subunit of class Ic ribonucleotide reductases (R2c) and in R2-like ligand-binding oxidases (R2lox). Although the protein-derived metal ligands are the same in both groups of proteins, the connectivity of the two metal ions and the chemistry each cofactor performs are different: in R2c, a one-electron oxidant, the Mn/Fe dimer is linked by two oxygen bridges (μ-oxo/μ-hydroxo), whereas in R2lox, a two-electron oxidant, it is linked by a single oxygen bridge (μ-hydroxo) and a fatty acid ligand. Here, we identified a second coordination sphere residue that directs the divergent reactivity of the protein scaffold. We found that the residue that directly precedes the N-terminal carboxylate metal ligand is conserved as a glycine within the R2lox group but not in R2c. Substitution of the glycine with leucine converted the resting-state R2lox cofactor to an R2c-like cofactor, a μ-oxo/μ-hydroxo–bridged MnIII/FeIII dimer. This species has recently been observed as an intermediate of the oxygen activation reaction in WT R2lox, indicating that it is physiologically relevant. Cofactor maturation in R2c and R2lox therefore follows the same pathway, with structural and functional divergence of the two cofactor forms following oxygen activation. We also show that the leucine-substituted variant no longer functions as a two-electron oxidant. Our results reveal that the residue preceding the N-terminal metal ligand directs the cofactor's reactivity toward one- or two-electron redox chemistry, presumably by setting the protonation state of the bridging oxygens and thereby perturbing the redox potential of the Mn ion

Composite InGaN/GaN/InAlN heterostructures emitting in the yellow-red spectral region

International audienceThe results of studies of the properties of composite InGaN/GaN/InAlN heterostructures are reported. It is shown that, in the InAlN layer, there is substantial phase separation that brings about the formation of three-dimensional islands consisting of AlN-InAlN-AlN regions. The dimensions of these islands depend on the thickness of the InAlN layer and the conditions of epitaxial growth. Interruptions in the growth of InAlN provide a means for influencing the structural properties of the InAlN islands. The use of composite InGaN/GaN/InAlN heterostructures, in which the InGaN layer with a high In content serves as the active region in light-emitting diode structures, makes it possible to achieve emission in the yellow-red wavelength range 560–620 nm

Single quantum well deep-green LEDs with buried InGaN/GaN short-period superlattice

International audienceIn spite of the great progress in III-N technology, LEDs with wavelength >530 nm still exhibit low efficiency compared to blue and short-wavelength-green LEDs. Here we report on significant improvement of deep-green LED properties by modifications of the structure design. The combination of InGaN/GaN superlattice followed by low-temperature GaN is the key element to increase the electroluminescence efficiency for deep-green LED. Various techniques were employed to clarify the correlation between structure properties, growth regimes and design. Modification of the defect structure of the GaN buffer by InGaN layers appears to be mostly responsible for the observed effect. LEDs processed and assembled in a standard flip-chip geometry with Ni–Ag p-contact demonstrate external quantum efficiencies of 8–20% in the 560–530 nm range

Transition from childhood to adulthood in coeliac disease: the Prague consensus report

The process of transition from childhood to adulthood is characterised by physical, mental and psychosocial development. Data on the transition and transfer of care in adolescents/young adults with coeliac disease (CD) are scarce. In this paper, 17 physicians from 10 countries (Sweden, Italy, the USA, Germany, Norway, the Netherlands, Australia, Britain, Israel and Denmark) and two representatives from patient organisations (Association of European Coeliac Societies and the US Celiac Disease Foundation) examined the literature on transition from childhood to adulthood in CD. Medline (Ovid) and EMBASE were searched between 1900 and September 2015. Evidence in retrieved reports was evaluated using the Grading of Recommendation Assessment, Development and Evaluation method. The current consensus report aims to help healthcare personnel manage CD in the adolescent and young adult and provide optimal care and transition into adult healthcare for patients with this disease. In adolescence, patients with CD should gradually assume exclusive responsibility for their care, although parental support is still important. Dietary adherence and consequences of non-adherence should be discussed during transition. In most adolescents and young adults, routine small intestinal biopsy is not needed to reconfirm a childhood diagnosis of CD based on European Society for Pediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) or North American Society for Pediatric Gastroenterology, Hepatology and Nutrition (NASPGHAN) criteria, but a biopsy may be considered where paediatric diagnostic criteria have not been fulfilled, such as, in a patient without biopsy at diagnosis, additional serology (endomysium antibody) has not been performed to confirm 10-fold positivity of tissue transglutaminase antibodies or when a no biopsy strategy has been adopted in an asymptomatic child