Glycans in infection: challenge and opportunity

Glycoconjugate vaccines are an important and successful means for prevention of infectious disease, including pneumoniae, meningitidis and salmonellosis. Understanding at atomic level the binding between microbial carbohydrates and specific functional monoclonal antibodies can direct vaccine design, particularly when synthetic carbohydrates are used. Recently, Dr Adamo has applied structural studies to identify the minimal epitope of group B Streptococcus type III polysaccharide (GBS PSIII). GBS PSIII is a leading cause of invasive infections in pregnant women, newborns, and elderly people, and the capsule is a major virulence factor targeted for vaccine development. GBS PSIII epitope has been historically considered the prototype of a complex conformational carbohydrate epitope. Through an integrated approach based on competitive ELISA/Surface Plasmon Resonance/Saturation Transfer NMR/X-ray he has elucidated a structural epitope consisting of a hexasaccharide constituted of a single repeating unit, and the glucosamine moiety of the next consecutive repeat unit. Based on this data, a conjugate vaccine from the short hexasaccharide epitope was prepared and elicited in mice functional antibodies comparably to a polysaccharide conjugate. Likewise, structural studies carried out for serotypes Ia and Ib showed that the polymeric nature of the polysaccharide can strongly impact epitope presentation.

A similar approach allowed the structural epitope of Neisseria meningitidis serogroup A and X, which are responsible for epidemic meningitis in the sub-Saharan region of Africa known as meningitis belt, to be mapped. Studies are ongoing to gain this type of information also on structurally similar sialylated W and Y polysaccharides. Structural data can be exploited to guide synthetic carbohydrate vaccine design. 

Dr Roberto Adamo, GSK, Italy

Dr Roberto Adamo, GSK, Italy

Roberto Adamo obtained his PhD in Pharmaceutical Science from the University of Catania (Italy) in 2003, working on the synthesis of biologically relevant inositols. After two post-doctoral fellowships at the NIH in Bethesda (USA) and at the Utrecht University (The Netherlands), in 2007 he joined Novartis where he was later appointed Head of the Carbohydrate Chemistry Laboratory and Leader of the Conjugation & Synthesis platform. Following the company acquisition by GSK, he has covered the role of Conjugation Platform Leader and Discovery Project Leader. Currently he is Vaccine Development Leader, working in translating discovery into clinics. His research interests vary from the synthesis of glycans, glycoconjugates and glyconanoparticles to structural glycobiology for the design of carbohydrate based therapeutics.

Staphylococcus aureus is a commensal bacterium that colonises about 30% of the population without any harmful effects. However, S. aureus also represents a major public health concern, due to its ability to cause a wide range of clinical infections combined with the alarming development of antibiotic resistance, which limits treatment options. One of the prime targets for the development of new therapeutic interventions against S. aureus are the wall teichoic acids (WTAs). WTAs are cell wall expressed glycopolymers that are critical for bacterial physiology, antibiotic resistance and colonisation. S. aureus WTAs display structural variation through glycosylation, resulting in three main glycotypes, which differently impact host-pathogen interaction. Through a multidisciplinary approach, including bacterial genetics, microbiology, immunology, and glycobiology, my group aims to unravel the molecular interplay between WTA glycotypes and host immunity to advance the development of new antimicrobial therapies. This presentation will highlight our findings related to the interaction of WTA glycotypes with innate receptors and human antibodies, which are critical components for front-line defense at barrier sites and long-term protection, respectively. 

Professor Nina van Sorge, Amsterdam UMC, the Netherlands

Professor Nina van Sorge, Amsterdam UMC, the Netherlands

Nina van Sorge is Professor of Translational Microbiology at the Department of Medical Microbiology and Infection Prevention at Amsterdam UMC, The Netherlands. Fundamental research in aims to clarify the molecular pathogenesis of bacterial infections to identify new strategies to prevent and treat these infections. She specifically focuses on the human pathogens Staphylococcus aureus and Streptococcus pyogenes (Strep A). She is co-inventor for a patent on Strep A vaccine development (WO 2013/020090 A3), which is currently in pre-clinical development. In addition to her research, she coordinates and leads the activities in the Netherlands Reference Laboratory for Bacterial Meningitis (NRLBM), which performs the national bacteriological surveillance for vaccine-preventable diseases caused by Neisseria meningitidis, Haemophilus influenzae b and Streptococcus pneumoniae as well as non-vaccine preventable invasive diseases caused by E. coli, Strep A and Streptococcus agalactiae (Strep B). The combination of fundamental research with molecular epidemiological surveillance provides a unique opportunity to gain insight into invasive bacterial infections at patient and population level.  

In this talk Dr van Kasteren will focus on his recent work looking at carbohydrate-lectin interactions at the single molecule level on living cells. These interactions play an important role in a wide diversity of biological processes, but are hard to quantify due to the low affinities of the interactions and the overlapping specificities of different lectins. To study this in more detail, particularly on immune cells, he has developed a point-accumulation in nanoscale topography (PAINT)-based super-resolution microscopy method that can be used to capture the weak glycan-lectin interactions at the single molecule level in living cells (glyco-PAINT). This has allowed Dr van Kasteren to obtain on rates and off rates for lectins, and he is now using this to dissect the role of glycan interactions on downstream immune activation events. Overall, Glyco-PAINT represents a powerful approach to study weak glycan-lectin interactions on the surface of living cells that can be potentially extended to a variety of lectin-sugar interactions.

Dr Sander van Kasteren, Universiteit Leiden, the Netherlands

Dr Sander van Kasteren, Universiteit Leiden, the Netherlands

The research of Sander van Kasteren bridges the fields of chemistry and immunology. After a PhD at the University of Oxford under Professor Benjamin G Davis, he did a Henry Wellcome Fellowship in the group of Professor Colin Watts, shifting to immunology. In 2012, he started his own group at Leiden University where he bridges these two fields. In 2014 he joined the institute of chemical immunology of which he is now the secretary. His research is aimed at understanding how post-translational modifications affect antigen presentation and T-cell activation, the process that underpins all adaptive immune responses. The angle he takes to study this is to use his chemical background to develop new chemical approaches to look at these processes. This work has been funded by multiple fellowships, including two ERC Grants. He was also awarded the 2012 Early Career Investigator Award by the British Biochemical Society.

Streptococcus agalactiae (Group B Strep, GBS), is one of the most common perinatal pathogens responsible for causing premature birth. Current therapeutic techniques aimed to ameliorate invasive GBS infections can result in complications in both the child and mother. To this end, the need for novel therapeutic options is urgent. Human milk oligosaccharides (HMOs) have been previously shown to possess antiadhesive and antimicrobial properties. To interrogate these characteristics, Professor Townsend examined HMO-mediated outcomes in both in vivo and ex vivo models of GBS infection using a murine model of ascending GBS infection, an EpiVaginalTM human organoid tissue model, and ex vivo human gestational membranes. Treatment with HMOs resulted in diminished adverse pregnancy outcomes, decreased GBS adherence to gestational tissues, decreased colonisation within the reproductive tract, and reduced in proinflammatory immune responses to GBS infection.

Professor Steve Townsend, Vanderbilt University, USA

Professor Steve Townsend, Vanderbilt University, USA

Steve was born and raised on the east side of Detroit. He completed his undergraduate education at Oakland University where he completed 4 years of research working on the synthesis of nucleoside radical precursors with Professor Amanda Bryant Friedrich. From there he matriculated to Vanderbilt University where he completed an education in Organic Chemistry, working on the synthesis of bielschowskysin under the mentorship of Professor Gary Sulikowski. Steve completed his education at Sloan Kettering Institute and Columbia University with Professor Sam Danishefsky, where he worked on the total synthesis of erythropoietin, pthrp, peptide ligation, and Diels-Alder methodology.

In 2014, Steve established an independent program at Vanderbilt University where his group leverages organic chemistry to address problems in human health, particularly in the areas of human milk science, antimicrobial agents, and chemotherapeutics.  He was promoted to Associate Professor with tenure in 2020 and in 2021 promoted to Stevenson Professor. Steve’s team has been honoured with a number of awards, including most recently,  the Sloan Research Fellowship, the Camille Dreyfus Teacher Scholar Award, The David Gin New Investigator Award from the ACS, the Ruth Kirstein Award for Excellence in Human Milk Science, and the C&E News Talented 12. Steve’s dedication to education is also highlighted by his Jeff Nordhaus Award for Excellence in Undergraduate Teaching and the DAPCEP community service award.

All most all eukaryotic cell surface and secreted proteins are modified by covalently-linked glycans which are essential mediators of biological processes such as protein folding, cell signalling, fertilisation, embryogenesis, and the proliferation of cells and their organisation into specific tissues. Overwhelming data supports the relevance of glycosylation in pathogen recognition, inflammation, innate immune responses, the development of autoimmune diseases, and cancer. It has, however, been difficult to explore biological properties of individual glycans because these bio-molecules are not readily available. To address this challenge, we have developed chemo-enzymatic methodologies that make it possible to prepare large libraries of highly complex glycans found on cells of interest. The synthetic approaches were employed to prepare a collection of glycans found on the upper airway of humans that were printed as a microarray to probe receptor specificities of several respiratory viruses. To validate the array data, cell surface engineering strategies were developed to place synthetic glycans on the surface of cells for gain of function studies. The technological platform made it possible to examine the evolution of receptor specificities of influenza H3N2 viruses and beta-corona viruses. Furthermore, it was employed to determine receptor specificities of Lassa virus. Knowledge of glycan receptor usage of zoonotic pathogens is making it possible to implement surveillance strategies to prevent future pandemics.

Professor Geert-Jan Boons, Universiteit Utrecht, the Netherlands

Professor Geert-Jan Boons, Universiteit Utrecht, the Netherlands

Geert-Jan Boons is the UGA Foundation Distinguished Professor in Biochemical Sciences at the Department of Chemistry and the Complex Carbohydrate Research Center (CCRC) of the University of Georgia (USA) and Professor and Chair of the Department of Medicinal and Biological Chemistry of Utrecht University (The Netherlands). He received a BS and PhD in Chemistry from Leiden University (the Netherlands) and was a postdoctoral fellow at Imperial College, London, and the University of Cambridge, and then as lecturer and professor at the University of Birmingham. In 1998, he joined the faculty of the Department of Chemistry and CCRC of the University of Georgia, and in 2015 he accepted a secondary academic appointment at Utrecht University (the Netherlands). His group is developing methods for synthesising exceptionally complex glycans and glycoconjugates that are being used for biological and biomedical explorations with a focus on infection, immunology and cancer.

Glycosylation is one of the most structurally and functionally diverse co- and post-translational modifications in a cell. This process is characterised by the addition and removal of glycans, especially to proteins and lipids, which have important implications in several biological processes. In mammals, the repeated enzymatic addition of a sialic acid unit to underlying sialic acids by polysialyltransferases, including ST8Sia2, leads to the formation of a sugar polymer called polysialic acid (polySia). The functional relevance of polySia has been extensively demonstrated in the nervous system. However, the role of polysialylation in infection is still little explored. Previous reports have shown that Trypanosoma cruzi (T. cruzi), a flagellated parasite that causes Chagas disease, changes host glycoproteins' sialylation. To understand the role of host polySia during T. cruzi infection, Associate Professor Palmisano used a combination of in silico and experimental tools. We observed that T. cruzi reduces the expression of the ST8Sia2 and the polysialylation of target substrates. He also found that chemical inhibition of ST8Sia2 reduced the parasite load in host cells. These findings suggest a novel approach to interfere with parasite infections through modulation of host polysialylation.

Associate Professor Giuseppe Palmisano, University of Sao Paulo, Brazil, and Macquarie University, Australia

Associate Professor Giuseppe Palmisano, University of Sao Paulo, Brazil, and Macquarie University, Australia

During his PhD at the University of Bari, Italy, Associate Professor Giuseppe Palmisano initially developed a method to analyse post-translational modifications (PTMs), particularly phosphorylation in protein complexes. During his postdoc at the Biochemistry and Molecular Biology Department, University of Southern Denmark, he developed mass spectrometry-based methods to analyse PTMs such as glycosylation, phosphorylation and oxidation as a tool to investigate the changes of these PTMs in several pathophysiological systems. A new method was developed to analyse sialylated glycopeptides. Moreover, novel chemical tags were developed to enrich specific PTMs such as O-GlcNacylated and cysteine oxidised peptides. Currently, he is associate professor at the Department of Parasitology, Institute of Biomedical Sciences, Brazil, and School of Natural Sciences, Macquarie University, Australia. His research activity focuses on the development of analytical and computational strategies to analyse PTMs in pathophysiological settings and understand the biological networks regulated. 

Urinary tract infections (UTI) belong to the most common infections worldwide and are predominantly caused by uropathogenic E. coli (UPEC). UPEC initiate the infection cycle by adhering to high-mannose glycoproteins on urothelial cells through their lectin FimH. Preventing the initial adhesion by blocking FimH offers a promising alternative to the conventional antibiotic treatment, which has become increasingly inefficacious due to antibiotic resistance.

The FimH-mannose interaction is shear stress dependent, meaning that FimH mediates medium binding at low shear stress and stronger binding at high shear stress. In the urinary tract, the shear stress-induced switch from medium- to the high-affinity becomes an effective tool for UPEC to evade clearance by the bulk flow of urine. By studying bacterial binding in a cell motility assay, we were able to show that these variants were highly mobile on a mannosylated surface, allowing optimal colonisation in the bladder. However, by switching to the high-affinity conformation, they can resist upcoming shear stress and are thus protected from being washed out through urination. In contrast, a variant locked in the high-affinity state, which is often used for in vitro and in vivo studies, formed long-lived interactions with mannose also in the absence of shear stress, rendering bacteria immobile.

It becomes evident that dynamic FimH variants are pathophysiologically favoured and represent the dominant therapeutic target. To further elucidate this conformational issue, antagonists with high affinities to both affinity states were synthesised and broadly characterised by extended ITC studies as well as in a mouse model.

Professor Beat Ernst, University of Basel, Switzerland

Professor Beat Ernst, University of Basel, Switzerland

Beat Ernst’s research interests are at the interface between carbohydrate chemistry and glycobiology, with a particular focus on the synthesis of glycomimetics and their pharmacological profiling. His research on one hand aims at understanding the conformational and structural requirements for biological activity of glycomimetics, and on the other hand, in collaboration with academic and industrial groups, he explores the therapeutic potential of such compounds in disease models, and in one case, in the clinic (Rivipansel, in clinical phase III for the treatment of sickle cell disease) with the ultimate goal to discover new therapeutics. His group is engaged in the synthesis of glycomimetics for numerous lectin targets (E-, P- and L-selectin, Siglec-2, -4, -7, -8 and -9 and FimH), and second evaluates and optimises the pharmacokinetic properties of test compounds.