Relaxed acceptor site specificity of bacterial oligosaccharyltransferase in vivo

A number of proteobacteria carry the genetic information to perform N-linked glycosylation, but only the protein glycosylation (pgl) pathway of Campylobacter jejuni has been studied to date. Here, we report that the pgl gene cluster of Campylobacter lari encodes for a functional glycosylation machinery that can be reconstituted in Escherichia coli. We determined that the N-glycan produced in this system consisted of a linear hexasaccharide. We found that the oligosaccharyltransferase (OST) of C. lari conserved a predominant specificity for the primary sequence D/E-X−1-N-X+1-S/T (where X−1 and X+1 can be any amino acid but proline). At the same time, we observed that this enzyme exhibited a relaxed specificity toward the acceptor site and modified asparagine residues of a protein at sequences DANSG and NNNST. Moreover, C. lari pgl glycosylated a native E. coli protein. Bacterial N-glycosylation appears as a useful tool to establish a molecular description of how single-subunit OSTs perform selection of glycosyl acceptor site

Relaxed acceptor site specificity of bacterial oligosaccharyltransferase in vivo

A number of proteobacteria carry the genetic information to perform N-linked glycosylation, but only the protein glycosylation (pgl) pathway of Campylobacter jejuni has been studied to date. Here, we report that the pgl gene cluster of Campylobacter lari encodes for a functional glycosylation machinery that can be reconstituted in Escherichia coli. We determined that the N-glycan produced in this system consisted of a linear hexasaccharide. We found that the oligosaccharyltransferase (OST) of C. lari conserved a predominant specificity for the primary sequence D/E-X−1-N-X+1-S/T (where X−1 and X+1 can be any amino acid but proline). At the same time, we observed that this enzyme exhibited a relaxed specificity toward the acceptor site and modified asparagine residues of a protein at sequences DANSG and NNNST. Moreover, C. lari pgl glycosylated a native E. coli protein. Bacterial N-glycosylation appears as a useful tool to establish a molecular description of how single-subunit OSTs perform selection of glycosyl acceptor site

Siglec receptors impact mammalian lifespan by modulating oxidative stress.

Aging is a multifactorial process that includes the lifelong accumulation of molecular damage, leading to age-related frailty, disability and disease, and eventually death. In this study, we report evidence of a significant correlation between the number of genes encoding the immunomodulatory CD33-related sialic acid-binding immunoglobulin-like receptors (CD33rSiglecs) and maximum lifespan in mammals. In keeping with this, we show that mice lacking Siglec-E, the main member of the CD33rSiglec family, exhibit reduced survival. Removal of Siglec-E causes the development of exaggerated signs of aging at the molecular, structural, and cognitive level. We found that accelerated aging was related both to an unbalanced ROS metabolism, and to a secondary impairment in detoxification of reactive molecules, ultimately leading to increased damage to cellular DNA, proteins, and lipids. Taken together, our data suggest that CD33rSiglecs co-evolved in mammals to achieve a better management of oxidative stress during inflammation, which in turn reduces molecular damage and extends lifespan

Galactosaminogalactan, a New Immunosuppressive Polysaccharide of Aspergillus fumigatus

A new polysaccharide secreted by the human opportunistic fungal pathogen Aspergillus fumigatus has been characterized. Carbohydrate analysis using specific chemical degradations, mass spectrometry, 1H and 13C nuclear magnetic resonance showed that this polysaccharide is a linear heterogeneous galactosaminogalactan composed of α1-4 linked galactose and α1-4 linked N-acetylgalactosamine residues where both monosacharides are randomly distributed and where the percentage of galactose per chain varied from 15 to 60%. This polysaccharide is antigenic and is recognized by a majority of the human population irrespectively of the occurrence of an Aspergillus infection. GalNAc oligosaccharides are an essential epitope of the galactosaminogalactan that explains the universal antibody reaction due to cross reactivity with other antigenic molecules containing GalNAc stretches such as the N-glycans of Campylobacter jejuni. The galactosaminogalactan has no protective effect during Aspergillus infections. Most importantly, the polysaccharide promotes fungal development in immunocompetent mice due to its immunosuppressive activity associated with disminished neutrophil infiltrates

Studies on the Detection, Expression, Glycosylation, Dimerization, and Ligand Binding Properties of Mouse Siglec-E

© 2017 by The American Society for Biochemistry and Molecular Biology, Inc. Published in the U.S.A. This is an Open Access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/)CD33-related Siglecs are a family of proteins widely expressed on innate immune cells. Binding of sialylated glycans or other ligands triggers signals that inhibit or activate inflammation. Immunomodulation by Siglecs has been extensively studied, but relationships between structure and functions are poorly explored. Here we present new data relating to the structure and function of Siglec-E, the major CD33-related Siglec expressed on mouse neutrophils, monocytes, macrophages, and dendritic cells. We generated nine new rat monoclonal antibodies specific to mouse Siglec-E, with no cross-reactivity to Siglec-F. Although all antibodies detected Siglec-E on transfected human HEK-293T cells, only two reacted with mouse bone marrow neutrophils by flow cytometry and on spleen sections by immunohistochemistry. Moreover, whereas all antibodies recognized Siglec-E-Fc on immunoblots, binding was dependent on intact disulfide bonds and N-glycans, and only two antibodies recognized native Siglec-E within spleen lysates. Thus, we further investigated the impact of Siglec-E homodimerization. Homology-based structural modeling predicted a cysteine residue (Cys-298) in position to form a disulfide bridge between two Siglec-E polypeptides. Mutagenesis of Cys-298 confirmed its role in dimerization. In keeping with the high level of 9-O-acetylation found in mice, sialoglycan array studies indicate that this modification has complex effects on recognition by Siglec-E, in relationship to the underlying structures. However, we found no differences in phosphorylation or SHP-1 recruitment between dimeric and monomeric Siglec-E expressed on HEK293A cells. Phylogenomic analyses predicted that only some human and mouse Siglecs form disulfide-linked dimers. Notably, Siglec-9, the functionally equivalent human paralog of Siglec-E, occurs as a monomer.Peer reviewedFinal Published versio

Pitfalls in machine learning‐based assessment of tumor‐infiltrating lymphocytes in breast cancer: a report of the international immuno‐oncology biomarker working group

The clinical significance of the tumor-immune interaction in breast cancer (BC) has been well established, and tumor-infiltrating lymphocytes (TILs) have emerged as a predictive and prognostic biomarker for patients with triple-negative (estrogen receptor, progesterone receptor, and HER2 negative) breast cancer (TNBC) and HER2-positive breast cancer. How computational assessment of TILs can complement manual TIL-assessment in trial- and daily practices is currently debated and still unclear. Recent efforts to use machine learning (ML) for the automated evaluation of TILs show promising results. We review state-of-the-art approaches and identify pitfalls and challenges by studying the root cause of ML discordances in comparison to manual TILs quantification. We categorize our findings into four main topics; (i) technical slide issues, (ii) ML and image analysis aspects, (iii) data challenges, and (iv) validation issues. The main reason for discordant assessments is the inclusion of false-positive areas or cells identified by performance on certain tissue patterns, or design choices in the computational implementation. To aid the adoption of ML in TILs assessment, we provide an in-depth discussion of ML and image analysis including validation issues that need to be considered before reliable computational reporting of TILs can be incorporated into the trial- and routine clinical management of patients with TNBC

Cardiovascular disease, chronic kidney disease, and diabetes mortality burden of cardiometabolic risk factors from 1980 to 2010: A comparative risk assessment

Background: High blood pressure, blood glucose, serum cholesterol, and BMI are risk factors for cardiovascular diseases and some of these factors also increase the risk of chronic kidney disease and diabetes. We estimated mortality from cardiovascular diseases, chronic kidney disease, and diabetes that was attributable to these four cardiometabolic risk factors for all countries and regions from 1980 to 2010. Methods: We used data for exposure to risk factors by country, age group, and sex from pooled analyses of population-based health surveys. We obtained relative risks for the effects of risk factors on cause-specific mortality from meta-analyses of large prospective studies. We calculated the population attributable fractions for each risk factor alone, and for the combination of all risk factors, accounting for multicausality and for mediation of the effects of BMI by the other three risks. We calculated attributable deaths by multiplying the cause-specific population attributable fractions by the number of disease-specific deaths. We obtained cause-specific mortality from the Global Burden of Diseases, Injuries, and Risk Factors 2010 Study. We propagated the uncertainties of all the inputs to the final estimates. Findings: In 2010, high blood pressure was the leading risk factor for deaths due to cardiovascular diseases, chronic kidney disease, and diabetes in every region, causing more than 40% of worldwide deaths from these diseases; high BMI and glucose were each responsible for about 15% of deaths, and high cholesterol for more than 10%. After accounting for multicausality, 63% (10·8 million deaths, 95% CI 10·1-11·5) of deaths from these diseases in 2010 were attributable to the combined effect of these four metabolic risk factors, compared with 67% (7·1 million deaths, 6·6-7·6) in 1980. The mortality burden of high BMI and glucose nearly doubled from 1980 to 2010. At the country level, age-standardised death rates from these diseases attributable to the combined effects of these four risk factors surpassed 925 deaths per 100 000 for men in Belarus, Kazakhstan, and Mongolia, but were less than 130 deaths per 100 000 for women and less than 200 for men in some high-income countries including Australia, Canada, France, Japan, the Netherlands, Singapore, South Korea, and Spain. Interpretation: The salient features of the cardiometabolic disease and risk factor epidemic at the beginning of the 21st century are high blood pressure and an increasing effect of obesity and diabetes. The mortality burden of cardiometabolic risk factors has shifted from high-income to low-income and middle-income countries. Lowering cardiometabolic risks through dietary, behavioural, and pharmacological interventions should be a part of the global response to non-communicable diseases. Funding: UK Medical Research Council, US National Institutes of Health. © 2014 Elsevier Ltd