Silicon abundance from RESIK solar flare observations

The RESIK instrument on the CORONAS-F spacecraft obtained solar flare and active region X-ray spectra in four channels covering the wavelength range 3.8 -- 6.1 \AA in its operational period between 2001 and 2003. Several highly ionized silicon lines were observed within the range of the long-wavelength channel (5.00 -- 6.05 \AA). The fluxes of the \sixiv Ly-$\beta$ line (5.217 \AA) and the \sixiii $1s^2 - 1s3p$ line (5.688 \AA) during 21 flares with optimized pulse-height analyzer settings on RESIK have been analyzed to obtain the silicon abundance relative to hydrogen in flare plasmas. As in previous work, the emitting plasma for each spectrum is assumed to be characterized by a single temperature and emission measure given by the ratio of emission in the two channels of GOES. The silicon abundance is determined to be $A({\rm Si}) = 7.93 \pm .21$ (\sixiv) and $7.89 \pm .13$ (\sixiii) on a logarithmic scale with H = 12. These values, which vary by only very small amounts from flare to flare and times within flares, are $2.6 \pm 1.3$ and $2.4 \pm 0.7$ times the photospheric abundance, and are about a factor of three higher than RESIK measurements during a period of very low activity. There is a suggestion that the Si/S abundance ratio increases from active regions to flares.Comment: To be published, Solar Physic

A Unique Resource for Solar Flare Diagnostic Studies: the SMM Bent Crystal Spectrometer

The {\em Bent Crystal Spectrometer}\/ (BCS) on the NASA {\em Solar Maximum Mission}\/ spacecraft observed the X-ray spectra of numerous solar flares during the periods 1980 February to November and 1984~--~1989. The instrument, the first of its kind to use curved crystal technology, observed the resonance lines of He-like Ca (\caxix) and Fe (\fexxv) and neighboring satellite lines, allowing the study of the rapid evolution of flare plasma temperature, turbulence, mass motions etc. To date there has not been a solar X-ray spectrometer with comparable spectral and time resolution, while subsequent solar cycles have delivered far fewer and less intense flares. The BCS data archive thus offers an unparalleled resource for flare studies. A recent re-assessment of the BCS calibration and its operations is extended here by using data during a spacecraft scan in the course of a flare on 1980 November~6 that highlights small deformations in the crystal curvature of the important channel~1 (viewing lines of \caxix\ and satellites). The results explain long-standing anomalies in spectral line ratios which have been widely discussed in the past. We also provide an in-flight estimation of the BCS collimator field of view which improves the absolute intensity calibration of the BCS. The BCS channel~1 background is shown to be entirely due to solar continuum radiation, confirming earlier analyses implying a time-variable flare abundance of Ca. We suggest that BCS high-resolution \caxix\ and \fexxv\ line spectra be used as templates for the analysis of X-ray spectra of non-solar sources.Comment: To be published, Astrophysical Journa

Cholesterol stimulates the lytic activity of Adenylate Cyclase Toxin on lipid membranes by promoting toxin oligomerization and formation of pores with a greater effective size

Several toxins acting on animal cells present different, but specific, interactions with cholesterol. Bordetella pertussis infects the human respiratory tract and causes whooping cough, a highly contagious and resurgent disease. Its virulence factor adenylate cyclase toxin (ACT) plays an important role in the course of infection. ACT is a pore-forming cytolysin belonging to the Repeats in ToXin (RTX) family of leukotoxins/hemolysins and is capable of permeabilizing several cell types and lipid vesicles. Previously, we observed that in the presence of cholesterol ACT induces greater liposome permeabilization. Similarly, recent reports also implicate cholesterol in the cytotoxicity of an increasing number of pore-forming RTX toxins. However, the mechanistic details by which this sterol promotes the lytic activity of ACT or of these other RTX toxins remain largely unexplored and poorly understood. Here, we have applied a combination of biophysical techniques to dissect the role of cholesterol in pore formation by ACT. Our results indicate that cholesterol enhances the lytic potency of ACT by promoting toxin oligomerization, a step which is indispensable for ACT to accomplish membrane permeabilization and cell lysis. Since our experimental design eliminates the possibility that this cholesterol effect derives from toxin accumulation due to lateral lipid phase segregation, we hypothesize that cholesterol facilitates lytic pore formation, by favoring a toxin conformation more prone to protein-protein interactions and oligomerization. Our data shed light on the complex relationship between lipid membranes and protein toxins acting on these membranes. Coupling cholesterol binding, increased oligomerization and increased lytic activity is likely pertinent for other RTX cytolysins.Rocío Alonso is gratefully acknowledged for excellent technical assistance. This study was supported by grants from the Spanish Ministerio de Economia y Competitividad BFU2017-82758-P (H.O.) and of Basque Government (Grupos Consolidados IT1264-19). D.G.B was recipients of a fellowship from the Bizkaia Biophysics Foundation, and JA was recipient of a fellowship from the Basque Government

A Systematic Approach to Assess the Activity and Classification of PCSK9 Variants

Background: Gain of function (GOF) mutations of PCSK9 cause autosomal dominant familial hypercholesterolemia as they reduce the abundance of LDL receptor (LDLR) more efficiently than wild-type PCSK9. In contrast, PCSK9 loss of function (LOF) variants are associated with a hypocholesterolemic phenotype. Dozens of PCSK9 variants have been reported, but most remain of unknown significance since their characterization has not been conducted. Objective: Our aim was to make the most comprehensive assessment of PCSK9 variants and to determine the simplest approach for the classification of these variants. Methods: The expression, maturation, secretion, and activity of nine well-established PCSK9 variants were assessed in transiently transfected HEK293 cells by Western blot and flow cytometry. Their extracellular activities were determined in HepG2 cells incubated with the purified recombinant PCSK9 variants. Their binding affinities toward the LDLR were determined by solid-phase immunoassay. Results: LDLR expression increased when cells were transfected with LOF variants and reduced when cells were transfected with GOF variants compared with wild-type PCSK9. Extracellular activities measurements yielded exactly similar results. GOF and LOF variants had increased, respectively reduced, affinities for the LDLR compared with wild-type PCSK9 with the exception of one GOF variant (R218S) that showed complete resistance to inactivation by furin. All variants were expressed at similar levels and underwent normal maturation and secretion patterns except for two LOF and two GOF mutants. Conclusions: We propose that transient transfections of HEK293 cells with a plasmid encoding a PCSK9 variant followed by LDLR expression assessment by flow cytometry is sufficient to reliably determine its GOF or LOF status. More refined experiments should only be used to determine the underlying mechanism(s) at hand.This work was supported by the Basque Government (Grupos Consolidados IT-1264-19). GL is supported by the Agence Nationale de la Recherche (Paris, France) Program Grant CHOPIN (CHolesterol Personalized Innovation) ANR-16-RHUS-0007 and Project Grant KRINGLE2 ANR-20-CE14-0009 as well as by La Fondation De France (FDF-00096274). U.G-G. was supported by Fundación Biofísica Bizkaia. A.B.-V. was supported by Programa de especialización de Personal Investigador Doctor en la UPV/EHU (2019) 2019-2020. A.L.-S. was supported by a grant PIF (2019–2020), Gobierno Vasco, and partially supported by Fundación Biofísica Bizkaia. KC and AKJ received a scholarship from the European Union (European Regional Development Fund INTERREG V) and the Région Réunion (Saint-Denis, Réunion, France)

Decellularization of xenografted tumors provides cell-specific in vitro 3D environment

In vitro cell culture studies are common in the cancer research field, and reliable biomimetic 3D models are needed to ensure physiological relevance. In this manuscript, we hypothesized that decellularized xenograft tumors can serve as an optimal 3D substrate to generate a top-down approach for in vitro tumor modeling. Multiple tumor cell lines were xenografted and the formed solid tumors were recovered for their decellularization by several techniques and further characterization by histology and proteomics techniques. Selected decellularized tumor xenograft samples were seeded with the HCC1806 human triple-negative breast cancer (TNBC) basal-like subtype cell line, and cell behavior was compared among them and with other control 2D and 3D cell culture methods. A soft treatment using Freeze-EDTA-DNAse allows proper decellularization of xenografted tumor samples. Interestingly, proteomic data show that samples decellularized from TNBC basal-like subtype xenograft models had different extracellular matrix (ECM) compositions compared to the rest of the xenograft tumors tested. The in vitro recellularization of decellularized ECM (dECM) yields tumor-type–specific cell behavior in the TNBC context. Data show that dECM derived from xenograft tumors is a feasible substrate for reseeding purposes, thereby promoting tumor-type–specific cell behavior. These data serve as a proof-of-concept for further potential generation of patient-specific in vitro research models.Grant RTI2018-101708-A-I00 funded by MCIN/AEI/10.13039/501100011033 and by ERDF A way of making Europe. Grants RYC2018-025502-I and PRE2018-084542 are funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. Grant MDM-2017-0720 Maria de Maeztu Units of Excellence Program funded by the Spanish State Research Agency. Grant KK-2019/00093 Elkartek program funded by Basque Government. Grant CICBMG_PhD_03_2021 funded by CICbiomaGUNE and Polymat. Grant CICBMG_PhD_05_2019 funded by CICbiomaGUNE and Polymat. 2019 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation, grant number IN[19]_CMA_BIO_0119. The BBVA Foundation accepts no responsibility for the opinions, statements, and contents included, which are entirely the responsibility of the authors

Half-BPS cosmic string in N=2 supergravity in the presence of a dilaton

We construct new half-BPS cosmic string solutions in D=4 N=2 supergravity compatible with a consistent truncation to N=1 supergravity where they describe D-term cosmic strings. The constant Fayet-Iliopoulos term in the N=1 D-term is not put in by hand but is geometrically engineered by a gauging in the mother N=2 supergravity theory. The coupling of the N=2 vector multiplets is characterized by a cubic prepotential admitting an axion-dilaton field, a common property of many compactifications of string theory. The axion-dilaton field survives the truncation to N=1 supergravity. On the string configuration the BPS equations constrain the dilaton to be an arbitrary constant. All the cosmic string solutions with different values of the dilaton have the same energy per unit length but different lenght scales.Comment: 52 pages; typos correcte

Kukutxeztula: "gainditutako" gaitz baten itzulera

Arnasbideetako infekzioek heriotza tasa altuak eragiten dituzte munduan, COVID-19 birusa izanik azken urteetako adibiderik argiena. Hala ere, ez da libre dabilen patogeno bakarra eta berrikuspen honetan Bordetella pertussis bakterio patogenoak eragindako kukutxeztulaz arituko gara. Kukutxeztula arnasbideen infekzio larri eta kutsakorra da, bertako jariakinekin edota listu tantekin kontaktua izatean transmititzen dena. Helduetan arrisku berezirik ez duten sintomak eragiten dituen arren (etengabeko eztul gertakariak, arnasteko zailtasuna edota sukarra, besteak beste), heriotza eragin dezake urte batetik beherako haurretan batez ere. Kukutxeztula fase goiztiar batean gainditu ez duten gaixoek bigarren mailako pneumonia bezalako konplikazioak garatu ditzakete, horixe izaten delarik kukutxeztulaz hiltzen diren gehienen arrazoi nagusia. Lehen txertoa garatu zenetik kontrolpean zegoela uste izan den arren, kalte handiak eragin ditu garapen bidean dauden herrialdeetan batez ere. Herrialde garatuetan ere badu bere inpaktua, eta 2011tik gaur arte Ipar Amerikan eta mendebaldeko Europan epidemia egoera zabaldu da. Berrikuspen honetan kukutxeztulari buruzko informazioaren eguneratze bat aurkezten da, B. pertussisek erabiltzen dituen hainbat mekanismo infekziosotan arreta jarriz. Mekanismo hauen oinarri molekularra ulertzeak lagundu dezake zeluletan gertatzen diren beste hainbat prozesuren ulerkeran, gaixotasunaren aurkako sendagai berrien garapenean edota biologia molekularreko tresna berrien garapenean.; Respiratory infections cause high mortality rates throughout the world, being the COVID-19 virus the clearest example in recent years. However, there are other several pathogens not fully controlled and in this review we will focus on whooping cough, the sickness caused by the pathogenic bacterium Bordetella pertussis.Whooping cough is a severe and contagious respiratory infection that is transmitted by coming into contact with local secretions or with saliva drops. Despite the symptoms are not of special risks for adults (continuous episodes of cough, difficulty breathing or fever), it can cause death especially in children younger than one year of age. Patients who have not overcome cough at an early stage may develop complications such as secondary pneumonia, which is the main cause of most who die with whooping cough. Although since the development of the first vaccine it has been considered to be under control, whooping cough has caused significant damage especially in developing countries. Surprisingly, it has also an impact on developed countries and since 2011 the epidemic has spread in North America and Western Europe. This review presents an update on whooping cough, focusing on the different infective mechanisms used by B.pertussis. Understanding of the molecular basis of these mechanisms may contribute to the understanding of other cellular processes, the development of new anti-disease drugs or the development of new molecular biology instruments

Site-specific O-glycosylation of members of the low-density lipoprotein receptor superfamily enhances ligand interactions

15 pags, 8 figs, 1 tab. -- This article contains supplementary material (Table S1, Figs. S1–S4, and Data Sets S1–S4.1)The low-density lipoprotein receptor (LDLR) and related receptors are important for the transport of diverse biomolecules across cell membranes and barriers. Their functions are especially relevant for cholesterol homeostasis and diseases, including neurodegenerative and kidney disorders. Members of the LDLR-related protein family share LDLR class A (LA) repeats providing binding properties for lipoproteins and other biomolecules. We previously demonstrated that short linker regions between these LA repeats contain conserved O-glycan sites. Moreover, we found that O-glycan modifications at these sites are selectively controlled by the GalNAc-transferase isoform, GalNAc-T11. However, the effects of GalNAc-T11–mediated O-glycosylation on LDLR and related receptor localization and function are unknown. Here, we characterized O-glycosylation of LDLR-related proteins and identified conserved O-glycosylation sites in the LA linker regions of VLDLR, LRP1, and LRP2 (Megalin) from both cell lines and rat organs. Using a panel of gene-edited isogenic cell line models, we demonstrate that GalNAc-T11–mediated LDLR and VLDLR O-glycosylation is not required for transport and cell-surface expression and stability of these receptors but markedly enhances LDL and VLDL binding and uptake. Direct ELISA-based binding assays with truncated LDLR constructs revealed that O-glycosylation increased affinity for LDL by 5-fold. The molecular basis for this observation is currently unknown, but these findings open up new avenues for exploring the roles of LDLR-related proteins in disease.This work was supported by the Læge Sofus Carl Emil Friis og hustru Olga Doris Friis’ Legat, the Kirsten og Freddy Johansen Fonden, the Lundbeck Foundation, the A.P. Møller og Hustru Chastine Mc-Kinney Møllers Fond til Almene Formaal, the Mizutani Foundation, the Novo Nordisk Foundation, the Danish Research Council Sapere Aude Research Talent Grant (to K. T. S.), and the Danish National Research Foundation (DNRF107). The authors declare that they have no conflicts of interest with the contents of this articl