Nucleotide excision repair (NER) is responsible for the removal of a large variety of structurally diverse DNA lesions. Mutations of the involved proteins cause the xeroderma pigmentosum (XP) cancer ...predisposition syndrome. Although the general mechanism of the NER process is well studied, the function of the XPA protein, which is of central importance for successful NER, has remained enigmatic. It is known, that XPA binds kinked DNA structures and that it interacts also with DNA duplexes containing certain lesions, but the mechanism of interactions is unknown. Here we present two crystal structures of the DNA binding domain (DBD) of the yeast XPA homolog Rad14 bound to DNA with either a cisplatin lesion (1,2-GG) or an acetylaminofluorene adduct (AAF-dG). In the structures, we see that two Rad14 molecules bind to the duplex, which induces DNA melting of the duplex remote from the lesion. Each monomer interrogates the duplex with a β-hairpin, which creates a 13mer duplex recognition motif additionally characterized by a sharp 70° DNA kink at the position of the lesion. Although the 1,2-GG lesion stabilizes the kink due to the covalent fixation of the crosslinked dG bases at a 90° angle, the AAF-dG fully intercalates into the duplex to stabilize the kinked structure.
Due to the great importance of palladium-catalyzed Heck-type reactions in scientific and industrial chemistry, a lot of publications and reviews have been published during the last years describing ...this matter under different aspects. This article presents a summary of catalytic applications of palladium complexes with phosphorus ligands containing a metallated sp
3-carbon centre (“palladacycles”) or with
N-heterocyclic carbene ligands in C–C and C–N coupling reactions of aryl halides including recent results of mechanistic discussions about their role in the catalytic cycle.
This article presents a summary of recent developments in the application of tri-
o- ligands as catalysts in Heck type reactions. During the last decade both types of palladium complexes have proven to be very efficient catalyst precursors in C–C and C–N coupling tolylphosphine bound palladacycles and palladium complexes with
N-heterocyclic carbene reactions even with deactivated aryl halides.
Modern aeroengine designs strive for peak specific fuel and thermal efficiency. To achieve these goals, engines have more highly loaded compressor stages, thinner aerofoils, and blended titanium ...integrated disks (blisks) to reduce weight. These configurations promote the occurrence of aeroelastic phenomena such as flutter. Two important parameters known to influence flutter stability are the reduced frequency and the ratio of plunge and pitch components in a combined flap mode shape. These are used as design criteria in the engine development process. However, the limit of these criteria is not fully understood. The following research aims to bridge the gap between semi-analytical models and modern compressors by systematically investigating the flutter stability of a linear compressor cascade. This paper introduces the plunge-to-pitch incidence ratio, which is defined as a function of reduced frequency and pitch axis setback for a first flap (1F) mode shape. Using numerical simulations, in addition to experimental validation, aerodynamic damping is computed for many modes to build stability maps. The results confirm the importance of these two parameters in compressor aeroelastic stability as well as demonstrate the significance of the plunge-to-pitch incidence ratio for predicting the flutter limit.
During endochondral ossification, the secreted growth factor Indian hedgehog (Ihh) regulates several differentiation steps. It interacts with a second secreted factor, parathyroid hormone-related ...protein (PTHrP), to regulate the onset of hypertrophic differentiation, and it regulates chondrocyte proliferation and ossification of the perichondrium independently of PTHrP. To investigate how the Ihh signal is translated in the different target tissues, we analyzed the role of the zinc-finger transcription factor Gli3, which acts downstream of hedgehog signals in other organs. Loss of Gli3 in Ihh mutants restores chondrocyte proliferation and delays the accelerated onset of hypertrophic differentiation observed in Ihh â/â mutants. Furthermore the expression of the Ihh target genes patched ( Ptch) and PTHrP is reactivated in Ihh â/â ;Gli3 â/â mutants. Gli3 seems thus to act as a strong repressor of Ihh signals in regulating chondrocyte differentiation. In addition, loss of Gli3 in mice that overexpress Ihh in chondrocytes accelerates the onset of hypertrophic differentiation by reducing the domain and possibly the level of PTHrP expression. Careful analysis of chondrocyte differentiation in Gli3 â/â mutants revealed that Gli3 negatively regulates the differentiation of distal, low proliferating chondrocytes into columnar, high proliferating cells. Our results suggest a model in which the Ihh/Gli3 system regulates two distinct steps of chondrocyte differentiation: (1) the switch from distal into columnar chondrocytes is repressed by Gli3 in a PTHrP-independent mechanism; (2) the transition from proliferating into hypertrophic chondrocytes is regulated by Gli3-dependent expression of PTHrP . Furthermore, by regulating distal chondrocyte differentiation, Gli3 seems to position the domain of PTHrP expression.
The tonoplastic inositol transporter INT1 is the only known transport protein in Arabidopsis that facilitates
-inositol import from the vacuole into the cytoplasm. Impairment of the release of ...vacuolar inositol by knockout of INT1 results in a severe inhibition of cell elongation in roots as well as in etiolated hypocotyls. Importantly, a more strongly reduced cell elongation was observed when sucrose was supplied in the growth medium, and this sucrose-dependent effect can be complemented by the addition of exogenous
-inositol. Comparing
mutants (defective in transport) with mutants defective in
-inositol biosynthesis (
mutants) revealed that the sucrose-induced inhibition in cell elongation does not just depend on inositol depletion. Secondary effects as observed for altered availability of inositol in biosynthesis mutants, as disturbed membrane turnover, alterations in PIN protein localization or alterations in inositol-derived signaling molecules could be ruled out to be responsible for impairing the cell elongation in
mutants. Although the molecular mechanism remains to be elucidated, our data implicate a crucial role of INT1-transported
-inositol in regulating cell elongation in a sucrose-dependent manner and underline recent reports of regulatory roles for sucrose and other carbohydrate intermediates as metabolic semaphores.
Visceral myopathies are debilitating conditions characterized by dysfunction of smooth muscle in visceral organs (bowel, bladder, and uterus). Individuals affected by visceral myopathy experience ...feeding difficulties, growth failure, life-threatening abdominal distension, and may depend on intravenous nutrition for survival. Unfortunately, our limited understanding of the pathophysiology of visceral myopathies means that current therapies remain supportive, with no mechanism-based treatments. We developed a patient-derived iPSC line with a c.769C > T p.R257C/+ mutation, the most common genetic cause of visceral myopathy. This cell line will facilitate studies of how the ACTG2 R257C heterozygous variant affects smooth muscle development and function.
Dysfunction of visceral smooth muscle (“visceral myopathy”) impairs bowel, bladder, and uterine function. Symptoms of this life-threatening condition include massive intestinal distension with slow ...transit, vomiting, feeding intolerance, growth failure, poor bladder emptying, and difficult vaginal delivery. The most common genetic cause of visceral myopathy is a heterozygous point mutation (R257C) in gamma smooth muscle actin (
ACTG2
). We genetically modified the WAe0009-A human embryonic stem cell line to carry the c.769C>T p.R257C/+ mutation. This cell line will facilitate studies of how the ACTG2 R257C heterozygous variant affects smooth muscle development and function.
Pathogens such as Staphylococcus aureus require iron to survive and have evolved specialized proteins to steal heme from their host. IsdC is the central conduit of the Isd (iron-regulated surface ...determinant) multicomponent heme uptake machinery; staphylococcal cell-surface proteins such as IsdA, IsdB, and IsdH are thought to funnel their molecular cargo to IsdC, which then mediates the transfer of the iron-containing nutrient to the membrane translocation system IsdDEF. The structure of the heme-IsdC complex reveals a novel heme site within an immunoglobulin-like domain and sheds light on its binding mechanism. The folding topology is reminiscent of the architecture of cytochrome f, cellobiose dehydrogenase, and ethylbenzene dehydrogenase; in these three proteins, the heme is bound in an equivalent position, but interestingly, IsdC features a distinct binding pocket with the ligand located next to the hydrophobic core of the β-sandwich. The iron is coordinated with a tyrosine surrounded by several non-polar side chains that cluster into a tightly packed proximal side. On the other hand, the distal side is relatively exposed with a short helical peptide segment that acts as a lip clasping onto almost half of the porphyrin plane. This structural feature is argued to play a role in the mechanism of binding and release by switching to an open conformation and thus loosening the interactions holding the heme. The structure of the heme-IsdC complex provides a template for the understanding of other proteins, such as IsdA, IsdB, and IsdH, that contain the same heme-binding module as IsdC, known as the NEAT (near transporter) domain.
A new player on the field: Carbocyclic carbenes are potentially better control ligands than N‐heterocyclic carbenes (NHCs) in catalyzed CC coupling reactions. PdII complexes of ...cycloheptatrienylidene (see picture), which are readily prepared, thermally stable, and highly stable towards acid, are as effective as the familiar NHC complexes in Suzuki and Heck reactions or perform even better.
Before and after: Crystal structures of the DNA (6‐4) photolyase from D. melanogaster—one structure in complex with DNA containing a (6‐4) lesion (see picture) and one in which the lesion has been ...repaired—provide new insight into lesion recognition and repair. The proposed mechanism for light‐induced, electron‐transfer‐based repair of the (6‐4) lesion does not proceed via an oxetane intermediate.
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