Sialyl-Tn (STn) is a disaccharide expressed by several solid tumours and is frequently reported as tumour-specific. This incomplete O-glycan arises from the dysregulation of glycosyltransferase activity, such as the sialyltransferase ST6GalNAc-I, favouring premature sialylation. Here, we aimed to review the literature for the prognostic value of STn across various cancers, as it remains unclear. Of the 25 selected studies reporting patient survival according to STn expression, STn was associated with worse survival in 14 studies, mostly in gastric, bladder, breast and sinonasal cancers. No impact was reported in 10 studies and the impact was uncertain in 2. We also inspected the STn protein carriers reported according to cancer type. Interestingly, while O-glycosylation is present in many cell surface proteins, only a few are described as STn carriers, with MUC1 mucin identified across several cancers. Yet the list of known STn carriers is likely increasing due to technology improvements. We also identified a striking diversity of antibodies used to identify STn, often with little information on their exact specificity, which may explain study divergences. The current review highlights the tumour-specific character of STn and its potential as a target for novel immunotherapies. However, challenges remain due to STn heterogeneous presentation and the need for standardization methods for its detection.
Glycans cover the surface of essentially all cells, giving rise to the so-called glycocalyx. Glycans, and particularly N-glycans are key players in defining the fate and the nature of the immune response, participating in both pro-inflammatory and anti-inflammatory pathways occurring in inflammation, autoimmunity and cancer. Glycans and glycan-binding proteins (GBPs) are instrumental molecules that integrate the immunological landscape in homeostasis, being involved in how the host immune system perceives the self and non-self. Perturbations in these immune regulatory circuits created by glycans and GBPs may result in the loss of immune tolerance associated with autoimmunity and inflammatory conditions, but also in malignant transformation. This chapter will discuss the regulatory role played by N-glycans as fundamental immune-checkpoints in the interplay between the immune cells and their surrounding microenvironment associated with homeostasis and disease. Furthermore, we will also explore how N-glycans can act as promising diagnostic and prognostic biomarkers in disease, as well as appealing targets for new therapeutic approaches in inflammation, autoimmunity and cancer.
The genus Mycobacterium comprises numerous species, including major human pathogens responsible for two diseases – tuberculosis and leprosy – that have afflicted humanity for millennia. Other Mycobacterium species are known to cause chronic lung infections, some of which spread through modern water distribution systems that they can colonize. Mycobacteria have a distinctive cell envelope that comprises a complex matrix of lipids, sugars, and lipoglycans, and which forms a formidable barrier against environmental stress and host immune responses, contributing to their resilience. They also possess two types of intracellular polymethylated polysaccharides, 6-O-methylglucose lipopolysaccharide (MGLP) and 3-O-methylmannose polysaccharide (MMP), which influence the synthesis of fatty acid precursors of envelope components. While in vitro studies have demonstrated their interactions with fatty acids and regulatory effects on fatty acid synthase activity, the precise in vivo functions remain elusive. MGLP has been implicated in heat stress adaptation, whereas MMP may play a role in cold stress responses. Although MGLP biosynthetic genes are conserved across mycobacterial genomes, a MMP biosynthetic gene cluster is absent in the important pathogens M. tuberculosis, M. leprae, and M. abscessus. MGLP biosynthesis follows a de novo pathway beginning with the glycoside glucosylglycerate (GG) and involving various gene clusters, whereas MMP biosynthesis seems to be governed by a single gene cluster encoding an MMP hydrolase that facilitates a self-recycling mechanism, generating oligomannoside primers for synthesis of new MMP. Despite gaps in our understanding of their physiological roles, particularly their impact on fatty acid metabolism and envelope integrity, and their restricted distribution, the enzymes in these pathways may represent promising targets for novel therapeutic interventions against mycobacterial infections, which remain pressing global health challenges.
The main hallmarks of Parkinson’s disease (PD) are the degeneration of nigral dopaminergic neurons and increased number of intracellular inclusions of aggregated α-synuclein called Lewy bodies. Mitochondrial dysfunction, oxidative stress, impaired proteostasis and neuroinflammation are strongly implicated in the pathogenesis of PD. Paralleled with the emergence of novel analytical methods and more sensitive tools, there has been increasing evidence revealing an association of aberrant glycosylation with PD. Here, we provide an overview of the most important cellular mechanisms implicated in the pathology of PD and explore aspects of dysfunctional or aberrant glycosylation establishing a link with the described pathological mechanisms for neurodegeneration. Some of the glycosylation pattern alterations described here have already been directly associated with pathological mechanisms of PD, while others are more generally associated with neurodegenerative diseases and could potentially have an impact on PD. Not intending to be an exhaustive review of all putative glycosylation modifications associated with PD, we selected classical proteins and pathways involved in different steps of the pathogenic process. The identification of these mechanisms will be crucial for the discovery of new therapeutic targets and pharmacological strategies based on glycans to afford neuroprotection in PD.
The LytR-CpsA-Psr (LCP) family of proteins plays a critical role in bacterial cell wall biosynthesis, specifically in the attachment of wall teichoic acids (WTAs) and other cell wall glycopolymers (CWGPs) to peptidoglycan. These CWGPs are essential components of the Gram-positive bacterial cell wall, contributing to its structural integrity, ion homeostasis, and resistance to environmental stress. By catalysing the covalent attachment of these polymers to the peptidoglycan layer, LCP proteins ensure the stability and function of the bacterial cell wall, which is critical for bacterial survival. This study presents a comprehensive structural analysis of experimentally determined LCP structures available and deposited in the Protein Data Bank (PDB) as well as AlphaFold2 models, revealing both conserved and variable features within the family. Our analysis focused on specific regions important for binding and activity on peptidoglycan substrates, such as the Mg²⁺ coordination site, active site, the hydrophobic pocket, and the peptidoglycan-binding groove. Despite low sequence identity, the analysis revealed high structural similarity among the proteins, particularly in the substrate binding sites and catalytic residues. This analysis provides a detailed understanding of the molecular determinants governing LCP protein function and their essential role in bacterial cell wall assembly, with potential implications for the development of novel antibacterial therapies.
One of the greatest challenges that industry faces in the 21st century is the transition from an economy based on fossil resources to one based on renewable resources. Biomass, which is widespread, abundant and inexpensive, is regarded as an ideal substitute for fossil resources. As a result, it is of great importance to look for efficient approaches to utilize biomass-derived carbohydrates as raw materials to produce value-added products. This chapter highlights selected examples of the most relevant value-added compounds, including furan derivatives, biofuels, amines, and bioplastics, obtained from biomass-derived carbohydrates.
Glycomic events could be the cause of the onset of many pathologies, some of them with imprecise diagnostics. Glycosylation is a post-translational modification of proteins where the resulting products, O-glycans and N-glycans located in the cell membrane (part of the cell glycome), as well as all the enzymatic machinery necessary for their processing, over- and under-expression (glycosyltransferases and glycosidases), constitute markers of a possible glycomic anomaly. The O- and N-glycan modifications are dependent on the specificity of the expressed enzymes involved in their biosynthesis and could result in loss of glycans, generation of truncated glycans or insertion of specific carbohydrates (fucose, sialic acid, galactose, mannose, lactose and others), increasing branching, which alters the cell glycomic profile. These insertions create different identities in the identification of diseases, such as cancer, diabetes, immunological, metabolic, and neurodegenerative diseases. Different diseases can express different glycosylated biomarkers. Ideally, they should be detected early. Early detection of glycan biomarkers requires highly accurate analytical methodologies, to establish an early diagnosis, which may mean a more favourable prognosis. Plant lectins are attractive proteins for use as molecular tools, as they exhibit unique specificities for glycans, and can detect alterations in the cell glycome that could be used to detected biomarkers of diseases.
Glycosylation is a ubiquitous modification, occurring in over 60% of eukaryotic proteins. It is the most complex post-translational modification of proteins and lipids, with an unparalleled capacity to generate diverse molecular structures. Glycosylation is a highly conserved enzymatic process catalysed by glycosyltransferases (GTs), involving the transfer of carbohydrate moieties to the side chains of specific amino acids in proteins, as well as to the ceramide group of lipids. This chapter is focused on the GTs involved in the O-glycosylation pathway, specifically in mucin-type O-glycosylation. Herein, the structural and molecular recognition features of key GTs implicated in the initial steps of mucin-type O-glycosylation are exhaustively described. Specifically, the enzymes with direct involvement in the formation of tumour-associated mucin O-glycans, such as GalNAc-Ts, C1GalT1, ST3Gal-I, ST6GalNAc-I, and -II are covered.
Every human cell is covered with a dense and complex array of sugar chains that impact a plethora of biological functions. In cancer, the cell surface witnesses a remodelling of these glycosidic protrusions involved in several cancer hallmarks. Moreover, this is often accompanied by the expression of altered proteoforms, resulting in distinct functions that contribute to tumour development and progression, and unique molecular signatures that may be explored for precision oncology and targeted therapeutics. In this chapter, we cover newly developed tools for the study of the cancer glycoproteome and glycan functionality. Namely, we address genetic engineering of glycogenes, novel glycoprotein-specific proteases, and bioorthogonal chemistry. State-of-the-art proteomic strategies are also described. Our goal is to provide an overview of the groundbreaking approaches that have accelerated our comprehension of glycosylation dynamics in cancer, outlining outstanding advancements towards clinical translation.
1,2-cis-Glycosides have both biological and chemical significance. Their presence in natural compounds influences taste, biological activity and drug development. Additionally, their syntheses provide avenues for chemical research and potential therapeutic applications. The construction of 1,2-cis-glycosidic bonds is still a major challenge in carbohydrate synthesis. Although most organic chemists crave general methods, glycosylation reactions continue to be a challenge. Since these reactions are highly dependent on the donor–acceptor pair, the solvent and reagents/catalysts/promoters, one should design the perfect donor and fine-tune the reaction conditions accordingly to obtain the desired stereochemical outcome. New methodologies and studies reveal solutions that may not be universal but can be the key to unsolved problems. In this chapter, recent methods for the synthesis of 1,2-cis-glycosides are highlighted.
The chapter deals with new activation conditions and technologies for glycosylation reactions with stereochemical and large-scale control. We describe new green activation conditions (electrochemistry, mechanochemistry, biocatalysis, continuous flow and photocatalysis) developed for increasing the efficiency of the chemical reactions and applied to glycosylation. Mechanochemistry and electrochemistry were applied to the synthesis of C-, N-, O-glycosides and nucleoside analogues. These conditions can be developed iteratively, without protection from glycosylated substrates. We also describe the use of continuous flow allowing better selectivity, shorter reaction times and easier scale-up, for example in the case of Remdesivir synthesis. Biocatalyzed reactions and photon-starved large-scale photo-redox reactions can be conducted under these conditions. Finally, automated synthesis is definitely entering glycomics. The opportunities for glycosylation provided by these new technologies are significant and respond to the increasing complexity of glycosidic targets.
Nucleosides have been extensively studied since the discovery of the structure and role of nucleic acids in biological processes. Several approaches have been developed to synthesize nucleosides and nucleoside analogues and, amongst them, the Sonogashira cross-coupling strategy has been a widely employed methodology. Hence, this review provides an overview of the synthesis of nucleosides and their analogues by the Sonogashira cross-coupling approach over the last three decades. Furthermore, the therapeutic relevance of the synthesized compounds will also be highlighted.
Carbohydrate-binding-modules (CBMs) are discrete auxiliary protein modules with a non-catalytic carbohydrate-binding function and that exhibit a great diversity of binding specificities. CBMcarb-DB is a curated database that classifies the three-dimensional structures of CBM–carbohydrate complexes determined by single-crystal X-ray diffraction methods and solution NMR spectroscopy. We designed the database architecture and the navigation tools to query the database with the Protein Data Bank (PDB), UniProtKB, and GlyTouCan (universal glycan repository) identifiers. Special attention was devoted to describing the bound glycans using simple graphical representation and numerical format for cross-referencing to other glycosciences and functional data databases. CBMcarb-DB provides detailed information on CBMs and their bound oligosaccharides and features their interactions using several open-access applications. We also describe how the curated information provided by CBMcarb-DB can be integrated with AI algorithms of 3D structure prediction, facilitating structure–function studies. Also in this chapter, we discuss the exciting convergence of CBMcarb-DB with the glycan array repository, which serves as a valuable resource for investigating the specific binding interactions between glycans and various biomolecular targets. The interaction of the two fields represents a significant milestone in glycosciences. CBMcarb-DB is freely available at https://cbmdb.glycopedia.eu/ and https://cbmcarb.webhost.fct.unl.pt.
Carbohydrates with a quaternary position are key players for designing nonnatural sugar derivatives with finely tuned biological properties. More particularly, compounds with a quaternary anomeric position show strong promises in glycobiology, but classical approaches to their preparation, where quaternarisation is performed before glycosylation, almost exclusively deliver a-ketopyranosides because of major drawbacks. Ketopyranosides in both and ß series could indeed be obtained by reversing the order of the key C–O and C–C bond-forming reactions. This quaternarization by insertion of a Rh(II)-carbene into the anomeric C–H bond was recently optimized to obtain lactones 7 and 8 in a-manno and ß-gluco series on preparative scale. Rh(II)-catalyzed decomposition of 5 and 6 is next performed in refluxing 1,2-dichloroethane to give lactones 7 and 8 by 1,5-C–H insertion of the highly reactive transient metallo-carbene.
Organogels are intriguing soft materials that can be obtained through the self-assembly of small molecules (organogelators). This self-assembly is the result of a precise balance of solvent/organogelator and organogelator/organogelator weak interactions. Sugar derivatives have played a key role in the design of organogelators as they provide several advantages in terms of availability and ease of functionalisation. Furthermore, they can bring some of the required weak interactions. This chapter gathers the major examples of small sugar-based organogelator structures and their ability to gel various types of organic solvents.
This chapter overviews the influence of radiation processing applied to thermoplastic starch and some other glucans in blends prepared with various types of plasticizers and additives. Our studies on the radiation-mediated modification of starch-based materials were primarily motivated by the pressing need for alternative sustainable plastics to reduce the environmental footprint of commodity polymers as structural and/or functional materials, particularly due to their use in packaging applications which represent about 40% of the global plastic production. We have started to explore the potentialities of electron beam irradiation applied to thermoplastic starch blends prepared with various composition in plasticizer and reactive additives, to improve the initial bulk and surface properties of the obtained materials and to limit the changes in structural features and mechanical performances with time. The reactivity of the blends submitted to radiation was studied in terms of kinetics and chemical mechanism to provide sufficient control over the transformations occurring at the molecular and macromolecular levels. The changes in physical and mechanical properties were correlated to the modifications performed by blending with reactive plasticizers and then with lignin and aromatic alcohols followed by irradiation at acceptable radiation dose to define conditions inducing significant improvements on the performances of the resulting thermoplastic material. The context of starch-based bioplastics as an alternative to synthetic polymer materials produced from fossil resources and from biomass is introduced at first. The key aspects of radiation treatments applied to polysaccharides are then summarized in terms of basic chemical reactivity and controlled adjustment of functional properties with respect to representative target applications. Electron beam irradiation of thermoplastic starch blends and of model compounds such as maltodextrin and maltotriose mixed with a selected reactive plasticizer, N-allylurea, was shown to yield blends exhibiting improved thermodynamic stability and reduced the rate of retrogradation upon ageing. Various types of lignin, aromatic alcohols and phenols with some structural features of lignin monomers were blended with starch and its model glucans to induce additional effects due the hydrophobicity of the additives. A strong influence of the aromatic additives and of glycerol on the response of the blends to irradiation was evidenced and quantified by measuring the changes of glucans molecular weight as a function of blends composition and of irradiation dose. The protective effect against radiation provided by the aromatic additives is emphasized and quantified by determining the changes in radiation chemical yields for scission G(S) and for cross-linking G(X) for hydro-alcoholic pullulan blends containing various amounts of cinnamyl alcohol.
The chemistry of l-rhamnose was studied already during the early days of carbohydrate chemistry because of its presence in many plant polysaccharides. Access to 6-deoxysugars requires deoxygenation at HO-6 in a hexose which, when d-perosamine is the target, is normally done through hydrogenolysis of a 6-bromo or 6-iodo derivative of d-mannose. The chapter describes deoxygenation at C-6 affected by the high-yielding redox rearrangement of benzylidene acetals, in n-octane. This protocol gives access to 6-deoxy sugar 3 in one step from the acetal 2, making it superior, in our opinion, to commonly used routes. Reactions were monitored by thin-layer chromatography (TLC) on silica gel 60 glass slides. Spots were visualized by charring with H2 SO4 in EtOH and/or UV light. Melting points were determined with a Kofler hot stage. Optical rotations were measured at ambient temperature with a Jasco P-2000 digital polarimeter.
Carbohydrate-modified nanomaterials are models for investigating medically relevant binding events. Preparation of glyco-nanoparticles is quite challenging, and various strategies have been employed for the synthesis of these molecular probes. Sugar-containing lipoic acid ligands are usually prepared as glycosylamide conjugates with unprotected carbohydrates. They are highly polar compounds which are difficult to purify. Reactions in organic media were carried out under nitrogen, and ACS-grade solvents were used without further purification. Reactions were monitored by thin-layer chromatography using silica gel F254-coated aluminum plates (Silicycle). Coupling constants are reported in Hertz, and the following abbreviations are used: singlet, doublet, doublet of doublets, triplet, multiplet, and broad. Assignments of NMR signals were made by homonuclear correlation spectroscopy and heteronuclear single quantum coherence two-dimensional spectroscopy.
Betulin, betulinic acid, and lupeol – pentacyclic triterpenoids belonging to the lupane family and easily accessible from the bark of Betula species – are interesting bioactive natural compounds due to their diverse pharmacological and biological properties. Nevertheless, poor hydrosolubility, as well as other pharmacokinetic parameters, limits their clinical applications. These problems can be addressed by the introduction of polar moieties at the C-3 and/or C-28 positions, e.g., by glycosylation to form saponins. The incorporation of a sugar moiety to the triterpene scaffold improves the pharmacological properties and water solubility by adding a hydrophilic carbohydrate fragment to the lupane core. Synthesis of natural and unnatural lupane-carbohydrate conjugates (saponins), as well as unwanted side reactions frequently observed during the glycosylation reaction, including acyl migration and the Wagner–Meerwein rearrangement, are discussed.
In the last decades, the use of enzymes for the conversion of lignocellulosic biomass into energy, materials, platform chemicals or bioactive molecules, namely the biorefinery, has emerged as a green alternative for a sustainable economy. Hemicelluloses, the second most abundant source of renewable carbon in plants, is mainly constituted of pentoses and represent an underutilized raw material with a high potential for the production of value-added compounds. Due to the numerous advantages of enzymes when compared to chemical catalysts, the use of hydrolytically-active hemicellulases as synthetic tools in glycosynthesis by reverse hydrolysis or transglycosylation reactions with activated substrates has become a very attractive area of research. This chapter proposes a global overview of the recent developments in the use of pentose-acting glycoside hydrolases: α-l-arabinofuranosidases, β-d-xylosidases and xylanases for the production of various pentosides with potential applications in different fields. A final part is also dedicated to lipases and their uses in the synthesis of pentose-based esters.
