Ubiquitous occurrence in Nature, abundant presence at strategically important places such as the cell surface and dynamic shifts in their profile by diverse molecular switches qualifies the glycans ...to serve as versatile biochemical signals. However, their exceptional structural complexity often prevents one noting how simple the rules of objective-driven assembly of glycan-encoded messages are. This review is intended to provide a tutorial for a broad readership. The principles of why carbohydrates meet all demands to be the coding section of an information transfer system, and this at unsurpassed high density, are explained. Despite appearing to be a random assortment of sugars and their substitutions, seemingly subtle structural variations in glycan chains by a sophisticated enzymatic machinery have emerged to account for their specific biological meaning. Acting as 'readers' of glycan-encoded information, carbohydrate-specific receptors (lectins) are a means to turn the glycans' potential to serve as signals into a multitude of (patho)physiologically relevant responses. Once the far-reaching significance of this type of functional pairing has become clear, the various modes of spatial presentation of glycans and of carbohydrate recognition domains in lectins can be explored and rationalized. These discoveries are continuously revealing the intricacies of mutually adaptable routes to achieve essential selectivity and specificity. Equipped with these insights, readers will gain a fundamental understanding why carbohydrates form the third alphabet of life, joining the ranks of nucleotides and amino acids, and will also become aware of the importance of cellular communication via glycan-lectin recognition.
Functional pairing of cellular glycoconjugates with tissue lectins is a highly selective process, whose determinative factors have not yet been fully delineated. Glycan structure and modes of ...presentation, that is, its position and density, can contribute to binding, as different members of a lectin family can regulate degrees of responsiveness to these factors. Using a peptide repeat sequence motif of the glycoprotein mucin-1, the principle of introducing synthetic (glyco)peptides with distinct variations in these three parameters to an array-based screening of tissue lectins is illustrated. Interaction profiles of seven adhesion/growth-regulatory galectins cover the range from intense signals with core 2 pentasaccharides and core 1 binding for galectins-3 and -5 to a lack of binding for galectin-1 and also the galectin-related protein, which was included as a negative control. Remarkably, the two tandem-repeat-type galectins-4 and -8 were distinguished by core 1 sialylation, as the two separated domains were. These results encourage further synthetic elaboration of the glycopeptide library and testing of the network of natural galectins and rationally engineered variants of the lectins.
What is the Sugar Code? Gabius, Hans‐Joachim; Cudic, Maré; Diercks, Tammo ...
ChemBioChem,
July 5, 2022, Letnik:
23, Številka:
13
Journal Article
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A code is defined by the nature of the symbols, which are used to generate information‐storing combinations (e. g. oligo‐ and polymers). Like nucleic acids and proteins, oligo‐ and polysaccharides ...are ubiquitous, and they are a biochemical platform for establishing molecular messages. Of note, the letters of the sugar code system (third alphabet of life) excel in coding capacity by making an unsurpassed versatility for isomer (code word) formation possible by variability in anomery and linkage position of the glycosidic bond, ring size and branching. The enzymatic machinery for glycan biosynthesis (writers) realizes this enormous potential for building a large vocabulary. It includes possibilities for dynamic editing/erasing as known from nucleic acids and proteins. Matching the glycome diversity, a large panel of sugar receptors (lectins) has developed based on more than a dozen folds. Lectins ‘read’ the glycan‐encoded information. Hydrogen/coordination bonding and ionic pairing together with stacking and C−H/π‐interactions as well as modes of spatial glycan presentation underlie the selectivity and specificity of glycan‐lectin recognition. Modular design of lectins together with glycan display and the nature of the cognate glycoconjugate account for the large number of post‐binding events. They give an entry to the glycan vocabulary its functional, often context‐dependent meaning(s), hereby building the dictionary of the sugar code.
Information coding by sugars: Letting symbols convey information comes in many forms such as the QR code. We explain that sugars are an ideal alphabet of life. They form an unsurpassed size of bio‐vocabulary. It is read and translated by a matching diversity of sugar receptors (lectins) so that establishing a dictionary for the glyco‐vocabulary is now in progress. The given QR code directs you to our review on the sugar code.
Multiple sclerosis (MS) is an inflammatory, demyelinating and neurodegenerative disease of the central nervous system with unknown etiology. Currently approved disease-modifying treatment modalities ...are immunomodulatory or immunosuppressive. While the applied drugs reduce the frequency and severity of the attacks, their efficacy to regenerate myelin membranes and to halt disease progression is limited. To achieve such therapeutic aims, understanding biological mechanisms of remyelination and identifying factors that interfere with remyelination in MS can give respective directions. Such a perspective is given by the emerging functional profile of galectins. They form a family of tissue lectins, which are potent effectors in processes as diverse as adhesion, apoptosis, immune mediator release or migration. This review focuses on endogenous and exogenous roles of galectins in glial cells such as oligodendrocytes, astrocytes and microglia in the context of de- and (re)myelination and its dysregulation in MS. Evidence is arising for a cooperation among family members so that timed expression and/or secretion of galectins-1, -3 and -4 result in modifying developmental myelination, (neuro)inflammatory processes, de- and remyelination. Dissecting the mechanisms that underlie the distinct activities of galectins and identifying galectins as target or tool to modulate remyelination have the potential to contribute to the development of novel therapeutic strategies for MS.
Trafficking of leukocytes and their local activity profile are of pivotal importance for many (patho)physiological processes. Fittingly, microenvironments are complex by nature, with multiple ...mediators originating from diverse cell types and playing roles in an intimately regulated manner. To dissect aspects of this complexity, effectors are initially identified and structurally characterized, thus prompting familial classification and establishing foci of research activity. In this regard, chemokines present themselves as role models to illustrate the diversification and fine-tuning of inflammatory processes. This in turn discloses the interplay among chemokines, their cell receptors and cognate glycosaminoglycans, as well as their capacity to engage in new molecular interactions that form hetero-oligomers between themselves and other classes of effector molecules. The growing realization of versatility of adhesion/growth-regulatory galectins that bind to glycans and proteins and their presence at sites of inflammation led to testing the hypothesis that chemokines and galectins can interact with each other by protein–protein interactions. In this review, we present some background on chemokines and galectins, as well as experimental validation of this chemokine–galectin heterodimer concept exemplified with CXCL12 and galectin-3 as proof-of-principle, as well as sketch out some emerging perspectives in this arena.
Glycan‐protein interactions play an important role in a broad range of physiological processes, raising interest to elucidate the structural interplay. Yet, their dynamic nature limits the analysis ...by crystallography, whereas NMR spectroscopy suffers from the low 1H dispersion of glycans. Therefore, their sparse fluorination and NMR screening by 1D Saturation Transfer Difference with relay to 19F (STDreF) was previously proposed to exploit the superior dispersion in 19F NMR spectroscopy. A new 2D STD‐TOCSYreF experiment is presented here that enables comprehensive epitope mapping of fluorinated glycans by combining the spectral resolution of 19F with the spatial resolution and coverage of 1H. For an illustration, the 2‐deoxy‐2‐fluoro derivative of the N‐glycan core trimannoside was synthesised and its recognition of Pisum sativum agglutinin by either of the two terminal mannose residues was confirmed. Going beyond the crystallographic information, the 2D STD‐TOCSYreF spectrum moreover visualised collateral contacts from the branching mannose and allowed to assess the ratio of both co‐existing binding modes through the α1,3‐ (67 %) and α1,6‐linked (33 %) terminal mannose moieties.
Glycan‐lectin recognition is involved in many (patho)physiological processes. Strategic 19F incorporation into the ligand enables comprehensive epitope mapping for lectin binding by the new 2D STD‐TOCSYreF (saturation transfer difference TOCSY with relay to 19F) NMR experiment, which combines the superior spectral resolution of 19F with the vast spatial resolution and coverage of 1H.
TIM‐3 has been considered as a target in cancer immunotherapy. In T cells, inhibitory as well as activating functions have been ascribed to this molecule. Its role may therefore depend on the state ...of T cells and on the presence of interaction partners capable to perform functional pairing. Carcinoembryonic antigen‐related cell adhesion molecule (CEACAM1) has been proposed to bind TIM‐3 and to regulate its function. Using a T cell reporter platform we confirmed CEACAM1‐mediated inhibition, but CEACAM1 did not functionally engage TIM‐3. TIM‐3 and CEACAM1 coexpression was limited to a small subset of activated T cells. Moreover, results obtained in extensive binding studies were not in support of an interaction between TIM‐3 and CEACAM1. Cytoplasmic sequences derived from TIM‐3 induced inhibitory signaling in our human T cell reporter system.
Our results indicate that TIM‐3 functions are independent of CEACAM1 and that this receptor has the capability to promote inhibitory signaling pathways in human T cells.
The role of TIM‐3 and CEACAM1 was studied in a T cell reporter system. CEACAM1–CEACAM1 interaction coinhibited T cell activation, whereas CEACAM1 did not functionally engage TIM‐3 in cis and in trans. A chimeric receptor system revealed inhibitory signaling via the cytoplasmic tail of TIM‐3
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Purpose
N‐Glycan profiling provides an indicator of the cellular potential for functional pairing with tissue lectins. Following the discovery of galectin expression by chondrocytes as a factor in ...osteoarthritis pathobiology, mapping of N‐glycans upon their phenotypic dedifferentiation in culture and in fibroblast‐like synoviocytes is a step to better understand glycobiological contributions to disease progression.
Experimental design
The profiles of cellular N‐glycans of human osteoarthritic chondrocytes and fibroblast‐like synoviocytes were characterized by mass spectrometry. RT‐qPCR experiments determined mRNA levels of 16 glycosyltransferases. Responsiveness of cells to galectins was quantified by measuring the mRNA level for interleukin‐1β.
Results
The shift of chondrocytes to a fibroblastic phenotype (dedifferentiation) is associated with changes in N‐glycosylation. The N‐glycan profile of chondrocytes at passage 4 reflects characteristics of synoviocytes. Galectins‐1 and ‐3 enhance expression of interleukin‐1β mRNA in both cell types, most pronounced in primary culture. Presence of interleukin‐1β leads to changes in sialylation in synoviocytes that favor galectin binding.
Conclusions and clinical relevance
N‐Glycosylation reflects phenotypic changes of osteoarthritic cells in vitro. Like chondrocytes, fibroblast‐like synoviocytes express N‐glycans that are suited to bind galectins, and these proteins serve as inducers of pro‐inflammatory markers in these cells. Synoviocytes can thus contribute to disease progression in osteoarthritis in situ.
Reticulocytes release small membrane vesicles termed exosomes during their maturation into erythrocytes. Exosomes are intraluminal vesicles of multivesicular endosomes released into the extracellular ...medium by fusion of these endosomal compartments with the plasma membrane. This secretion pathway contributes to reticulocyte plasma membrane remodeling by eliminating certain membrane glycoproteins. We show in this study that galectin-5, although mainly cytosolic, is also present on the cell surface of rat reticulocytes and erythrocytes. In addition, in reticulocytes, it resides in the endosomal compartment. We document galectin-5 translocation from the cytosol into the endosome lumen, leading to its secretion in association with exosomes. Galectin-5 bound onto the vesicle surface may function in sorting galactose-bearing glycoconjugates. Fittingly, we found that Lamp2, a major cellular glycoprotein presenting galectin-reactive poly-N-acetylactosamine chains, is lost during reticulocyte maturation. It is associated with released exosomes, suggestive of binding to galectin-5. Finally, we reveal that the uptake of rat reticulocyte exosomes by macrophages is dependent on temperature and the mechanoenzyme dynamin and that exosome uptake is decreased by adding galectin-5. These data imply galectin-5 functionality in the exosomal sorting pathway during rat reticulocyte maturation.
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