Facile synthesis of C‐terminal thioesters is integral to native chemical ligation (NCL) strategies for chemical protein synthesis. We introduce a new method of mild peptide activation, which ...leverages solid‐phase peptide synthesis (SPPS) on an established resin linker and classical heterocyclic chemistry to convert C‐terminal peptide hydrazides into their corresponding thioesters via an acyl pyrazole intermediate. Peptide hydrazides, synthesized on established trityl chloride resins, can be activated in solution with stoichiometric acetyl acetone (acac), readily proceed to the peptide acyl pyrazoles. Acyl pyrazoles are mild acylating agents and are efficiently exchanged with an aryl thiol, which can then be directly utilized in NCL. The mild, chemoselective, and stoichiometric activating conditions allow this method to be utilized through multiple sequential ligations without intermediate purification steps.
Mild acac‐tivation: Peptide hydrazides can be activated in solution with stoichiometric acetyl acetone (acac) to give the corresponding peptide acyl pyrazoles. These acyl pyrazoles can be transformed into peptide thioesters, which can then be directly used in native chemical ligation. The mild, chemoselective, and stoichiometric activating conditions allow this method to be used for multiple sequential ligations without intermediate purification steps.
Combining the precise parallaxes and optical photometry delivered by Gaia’s second data release with the photometric catalogues of Pan-STARRS1, 2MASS, and AllWISE, we derived Bayesian stellar ...parameters, distances, and extinctions for 265 million of the 285 million objects brighter than G = 18. Because of the wide wavelength range used, our results substantially improve the accuracy and precision of previous extinction and effective temperature estimates. After cleaning our results for both unreliable input and output data, we retain 137 million stars, for which we achieve a median precision of 5% in distance, 0.20 mag in V-band extinction, and 245 K in effective temperature for G ≤ 14, degrading towards fainter magnitudes (12%, 0.20 mag, and 245 K at G = 16; 16%, 0.23 mag, and 260 K at G = 17, respectively). We find a very good agreement with the asteroseismic surface gravities and distances of 7000 stars in the Kepler, K2-C3, and K2-C6 fields, with stellar parameters from the APOGEE survey, and with distances to star clusters. Our results are available through the ADQL query interface of the Gaia mirror at the Leibniz-Institut für Astrophysik Potsdam (gaia.aip.de) and as binary tables at data.aip.de. As a first application, we provide distance- and extinction-corrected colour-magnitude diagrams, extinction maps as a function of distance, and extensive density maps. These demonstrate the potential of our value-added dataset for mapping the three-dimensional structure of our Galaxy. In particular, we see a clear manifestation of the Galactic bar in the stellar density distributions, an observation that can almost be considered direct imaging of the Galactic bar.
Posttranslational modifications, typically small chemical tags attached on amino acids following protein biosynthesis, have a profound effect on protein structure and function. Numerous chemically ...and structurally diverse posttranslational modifications, including methylation, acetylation, hydroxylation, and ubiquitination, have been identified and characterised on lysine residues in proteins. In this feature article, we focus on chemical tools that rely on the site-specific incorporation of unnatural amino acids into peptides and proteins to probe posttranslational modifications of lysine. We highlight that simple amino acid mimics enable detailed mechanistic and functional assignment of enzymes that install and remove such modifications, and proteins that specifically recognise lysine posttranslational modifications.
Application of structurally and chemically diverse unnatural amino acids in biomolecular studies of lysine posttranslational modifications is described in this Feature Article.
•Pathogens employ versatile effector catalogs to deregulate host immunity.•Effectors are used by microbes throughout the symbiotic continuum.•Effectors modulate co-operation and competition in local ...microbiomes.•Rapid effector diversification is essential for microbial niche establishment.
Microorganisms play essential roles in almost every environment on earth. For instance, microbes decompose organic material, or establish symbiotic relationships that range from pathogenic to mutualistic. Symbiotic relationships have been particularly well studied for microbial plant pathogens and have emphasized the role of effectors; secreted molecules that support host colonization. Most effectors characterized thus far play roles in deregulation of host immunity. Arguably, however, pathogens not only deal with immune responses during host colonization, but also encounter other microbes including competitors, (myco)parasites and even potential co-operators. Thus, part of the effector catalog may target microbiome co-inhabitants rather than host physiology.
Context.
The large astrometric and photometric survey performed by the
Gaia
mission allows for a panoptic view of the Galactic disc and its stellar cluster population. Hundreds of stellar clusters ...were only discovered after the latest
Gaia
data release (DR2) and have yet to be characterised.
Aims.
Here we make use of the deep and homogeneous
Gaia
photometry down to
G
= 18 to estimate the distance, age, and interstellar reddening for about 2000 stellar clusters identified with
Gaia
DR2 astrometry. We use these objects to study the structure and evolution of the Galactic disc.
Methods.
We relied on a set of objects with well-determined parameters in the literature to train an artificial neural network to estimate parameters from the
Gaia
photometry of cluster members and their mean parallax.
Results.
We obtain reliable parameters for 1867 clusters. Our catalogue confirms the relative lack of old stellar clusters in the inner disc (with a few notable exceptions). We also quantify and discuss the variation of scale height with cluster age, and we detect the Galactic warp in the distribution of old clusters.
Conclusions.
This work results in a large and homogeneous cluster catalogue, allowing one to trace the structure of the disc out to distances of ∼4 kpc. However, the present sample is still unable to trace the outer spiral arm of the Milky Way, which indicates that the outer disc cluster census might still be incomplete.
Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise ...astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.
The liver is essential for inducing immunological tolerance toward harmless antigens to maintain immune system homeostasis. However, the precise cellular mechanisms of tolerance induction against ...particle‐bound antigens, the role of the local hepatic microenvironment, and implications for therapeutic targets in immune‐mediated diseases are currently unclear. In order to elucidate cellular mechanisms of tolerance induction in healthy and injured liver, we developed a novel in vivo system combining the systemic delivery of low‐dose peptide antigens coupled to inert particles, immunological readouts, and sophisticated intravital multiphoton microscopy‐based imaging of liver in mice. We show that liver resident macrophages, Kupffer cells (KCs), but not hepatic monocyte‐derived macrophages or dendritic cells (DCs), are the central cellular scavenger for circulating particle‐associated antigens in homeostasis. KC‐associated antigen presentation induces CD4 T‐cell arrest, expansion of naturally occurring Foxp3+CD25+ interleukin‐10‐producing antigen‐specific regulatory T cells (Tregs) and tolerogenic immunity. Particle‐associated tolerance induction in the liver protected mice from kidney inflammation in T‐cell‐mediated glomerulonephritis, indicating therapeutic potential of targeting KC for immune‐mediated extrahepatic disorders. Liver inflammation in two independent experimental models of chronic liver injury and fibrosis abrogated tolerance induction and led to an immunogenic reprogramming of antigen‐specific CD4 T cells. In injured liver, infiltrating monocyte‐derived macrophages largely augment the hepatic phagocyte compartment, resulting in antigen redistribution between myeloid cell populations and, simultaneously, KCs lose signature markers of their tolerogenic phenotype. Conclusions: Hepatic induction of tissue‐protective immunological tolerance against particulate antigens is dependent on KCs as well as on a noninflamed liver microenvironment, thereby providing mechanistic explanations for the clinical observation of immune dysfunction and tolerance break in patients with advanced liver diseases. (Hepatology 2015;62:279‐291)
The bacterial transpeptidase Sortase A (SrtA) is a surface enzyme of Gram-positive pathogenic bacteria. It has been shown to be an essential virulence factor for the establishment of various ...bacterial infections, including septic arthritis. However, the development of potent Sortase A inhibitors remains an unmet challenge. Sortase A relies on a five amino acid sorting signal (LPXTG), by which it recognizes its natural target. We report the synthesis of a series of peptidomimetic inhibitors of Sortase A based on the sorting signal, supported by computational binding analysis. By employing a FRET-compatible substrate, our inhibitors were assayed
in vitro
. Among our panel, we identified several promising inhibitors with IC
50
values below 200 μM, with our strongest inhibitor - LPRDSar - having an IC
50
of 18.9 μM. Furthermore, it was discovered that three of our compounds show an effect on growth and biofilm inhibition of pathogenic
Staphylococcus aureus
, with the inclusion of a phenyl ring seemingly key to this effect. The most promising compound in our panel, BzLPRDSar, could inhibit biofilm formation at concentrations as low as 32 μg mL
−1
, manifesting it as a potential future drug lead. This could lead to treatments for MRSA infections in clinics and diseases such as septic arthritis, which has been directly linked with SrtA.
A series of peptidomimetic Sortase A inhibitors is reported. These compounds show inhibition activity of the Sortase A enzyme and efficiently prevent biofilm formation of
S. aureus
.
SARS-CoV-2 Spike protein RBD interacts with the hACE2 receptor to initiate cell entry and infection. We set out to develop lactam-based
i,i
+ 4 stapled hACE2 peptides targeting SARS-CoV-2.
In vitro
...screening demonstrates the inhibition of the Spike protein RBD-hACE2 complex formation by the hACE2
21-55
A36K-F40E stapled peptide (IC
50
: 3.6 μM,
K
d
: 2.1 μM), suggesting that hACE2 peptidomimetics could form the basis for the development of anti-COVID-19 therapeutics.
Stapled hACE2 peptides inhibit the formation of the SARS-CoV-2-hACE2 complex, providing the basis for the development of anti-COVID-19 therapeutics.
Context. The Gaia Second Data Release provides precise astrometry and photometry for more than 1.3 billion sources. This catalog opens a new era concerning the characterization of open clusters and ...test stellar models, paving the way for better understanding of the disk properties. Aims. The aim of the paper is to improve the knowledge of cluster parameters, using only the unprecedented quality of the Gaia photometry and astrometry. Methods. We have made use of the membership determination based on the precise Gaia astrometry and photometry. We applied an automated Bayesian tool, BASE-9, to fit stellar isochrones on the observed G, GBP, GRP magnitudes of the high probability member stars. Results. We derive parameters such as age, distance modulus, and extinction for a sample of 269 open clusters, selecting only low reddening objects and discarding very young clusters, for which techniques other than isochrone-fitting are more suitable for estimating ages.
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