Glycolipids are glycoconjugates that are predominantly found on the extracellular surface of cells ranging from bacteria to men. In bacteria and plants, glycoglycerolipids represent the main ...glycolipid species. Ceramides as carrier for glycans, termed glycosphingolipids (GSLs), are characteristic for vertebrates and insects. The glycan part is involved in a variety of biological activities including cell adhesion and initiation of signaling. Most of these functions rest on two basic principles: (1) GSLs spontaneously contribute to organize lipid rafts in biological membranes, thereby forming functional complexes (‘glycosynapses’) with receptor proteins and ion channels and (2) their glycans are bound by receptors like galectins (protein–glycan recognition) or cognate glycans (glycan–glycan recognition). This interaction modulates cell adhesion, differentiation and growth processes. Besides their contribution to normal cell behavior, GSL expression patterns also influence disease processes by inducing cellular malfunctions when aberrant, as highlighted by inherited disorders of GSL metabolism like sphingolipidoses. Altered GSL patterns are also associated with common neurological diseases, autoimmune diseases and cancer. With respect to infections, various GSL-presented glycans are attachment sites for bacteria and viruses as well as primary targets for bacterial toxins. This review provides an introduction to GSL structures, their nomenclature and metabolism. Building on this, normal and pathological functions of GSL will be surveyed.
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.
Galectin-4 (Gal4) has been suggested to function as a tumor suppressor in colorectal cancer (CRC). In order to systematically explore its function in CRC, we established a CRC cell line where Gal4 ...expression can be regulated via the doxycycline (dox)-inducible expression of a single copy wildtype LGALS4 transgene generated by recombinase-mediated cassette exchange (RMCE). Using this model and applying in-depth proteomic and phosphoproteomic analyses, we systematically screened for intracellular changes induced by Gal4 expression. Overall, 3083 cellular proteins and 2071 phosphosites were identified and quantified, of which 1603 could be matched and normalized to their protein expression levels. A bioinformatic analysis revealed that most of the regulated proteins and phosphosites can be localized in the nucleus and are categorized as nucleic acid-binding proteins. The top candidates whose expression was modulated by Gal4 are PURB, MAPKAPK3, BTF3 and BCAR1, while the prime candidates with altered phosphorylation included ZBTB7A, FOXK1, PURB and CK2beta. In order to validate the (phospho)proteomic data, we confirmed these candidates by a radiometric metabolic-labelling and immunoprecipitation strategy. All candidates exert functions in the transcriptional or translational control, indicating that Gal4 might be involved in these processes by affecting the expression or activity of these proteins.
Recognition of glycans by lectins is emerging as (patho)physiologically broadly used mode of cellular information transfer. Whereas the direct ligand-receptor contact is often already thoroughly ...characterized, the functional relevance of aspects of architecture such as modular design and valence of lectins is less well defined.
Following an introduction to modular lectin design, three levels of methodology are then reviewed that delineate lectin structure-activity relationships beyond glycan binding, with emphasis on domain shuffling.
Engineering of variants by modular transplantation facilitates versatile Nature-inspired design switches and access to new combinations with translational potential, as exemplified for human adhesion/growth-regulatory galectins.
To gain an understanding of the functional significance of natural variations in quaternary structure and modular design within a protein family is a current challenge. Strategic application of methods of the described phases is a means to respond to this challenge.
•Lectins have distinct types of design of not yet known functional significance.•Chemical modifications are a means to alter quaternary structure and cross-linking.•Site-specific sequence changes generate lectins with new specificity.•Modular transplantations generate lectin variants with new design and function.•Human lectin variants have innovative potential for therapy.
Glycan-lectin recognition is assumed to elicit its broad range of (patho)physiological functions via a combination of specific contact formation with generation of complexes of distinct ...signal-triggering topology on biomembranes. Faced with the challenge to understand why evolution has led to three particular modes of modular architecture for adhesion/growth-regulatory galectins in vertebrates, here we introduce protein engineering to enable design switches. The impact of changes is measured in assays on cell growth and on bridging fully synthetic nanovesicles (glycodendrimersomes) with a chemically programmable surface. Using the example of homodimeric galectin-1 and monomeric galectin-3, the mutual design conversion caused qualitative differences, i.e., from bridging effector to antagonist/from antagonist to growth inhibitor and vice versa. In addition to attaining proof-of-principle evidence for the hypothesis that chimera-type galectin-3 design makes functional antagonism possible, we underscore the value of versatile surface programming with a derivative of the pan-galectin ligand lactose. Aggregation assays with N,N′-diacetyllactosamine establishing a parasite-like surface signature revealed marked selectivity among the family of galectins and bridging potency of homodimers. These findings provide fundamental insights into design-functionality relationships of galectins. Moreover, our strategy generates the tools to identify biofunctional lattice formation on biomembranes and galectin-reagents with therapeutic potential.
Chemical and biological tools are harnessed to investigate the impact of spatial factors for functional pairing of human lectins with counterreceptors. The homodimeric adhesion/growth‐regulatory ...galectin‐1 and a set of covalently linked homo‐oligomers from di‐ to tetramers serve as proof‐of‐principle test cases. Glycodendrimersomes provide a versatile and sensitive diagnostic platform to reveal thresholds for ligand density and protein concentration in aggregation assays (trans‐activity), irrespective of linker length between lectin domains. Monitoring the affinity of cell binding and ensuing tumor growth inhibition reveal the linker length to be a bidirectional switch for cis‐activity. The discovery that two aspects of lectin functionality (trans‐ versus cis‐activity) respond non‐uniformly to a structural change underscores the power of combining synthetic and biological tools to advance understanding of the sugar functionality of the cell surface.
Carbohydrate‐directed cell adhesion: Chemical programming of the glycan presentation of glycodendrimersomes (GDSs) and the responsiveness of cells to lectin binding have been combined to define the structure–activity relationships for trans‐bridging and cis‐crosslinking of human lectins. Consequences of structural engineering of both lectin and glycan topology are explored and quantified (Gal‐1=galectin‐1).
What is the Sugar Code? Gabius, Hans‐Joachim; Cudic, Maré; Diercks, Tammo ...
Chembiochem : a European journal of chemical biology,
July 5, 2022, Letnik:
23, Številka:
13
Journal Article
Recenzirano
Odprti dostop
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.
Human macrophage galactose-type lectin (hMGL, HML, CD301, CLEC10A), a C-type lectin expressed by dendritic cells and macrophages, is a receptor for N-acetylgalactosamine α-linked to serine/threonine ...residues (Tn antigen, CD175) and its α2,6-sialylated derivative (sTn, CD175s). Because these two epitopes are among malignant cell glycan displays, particularly when presented by mucin-1 (MUC1), assessing the influence of the site and frequency of glycosylation on lectin recognition will identify determinants governing this interplay. Thus, chemical synthesis of the tandem-repeat O-glycan acceptor region of MUC1 and site-specific threonine glycosylation in all permutations were carried out. Isothermal titration calorimetry (ITC) analysis of the binding of hMGL to this library of MUC1 glycopeptides revealed an enthalpy-driven process and an affinity enhancement of an order of magnitude with an increasing glycan count from 6–8 μM for monoglycosylated peptides to 0.6 μM for triglycosylated peptide. ITC measurements performed in D2O permitted further exploration of the solvation dynamics during binding. A shift in enthalpy–entropy compensation and contact position-specific effects with the likely involvement of the peptide surroundings were detected. KinITC analysis revealed a prolonged lifetime of the lectin–glycan complex with increasing glycan valency and with a change in the solvent to D2O.
Patients with sepsis-associated delirium (SAD) show severe neurological impairment, often require an intensive care unit (ICU) stay and have a high risk of mortality. Hence, useful biomarkers for ...early detection of SAD are urgently needed. Extracellular vesicles (EVs) and their cargo are known to maintain normal physiology but also have been linked to numerous disease states. Here, we sought to identify differentially expressed proteins in plasma EVs from SAD patients as potential biomarkers for SAD. Plasma EVs from 11 SAD patients and 11 age-matched septic patients without delirium (non-SAD) were isolated by differential centrifugation, characterized by nanoparticle tracking analysis, transmission electron microscopy and Western blot analysis. Differential EV protein expression was determined by mass spectrometry and the resulting proteomes were characterized by Gene Ontology term and between-group statistics. As preliminary results because of the small group size, five distinct proteins showed significantly different expression pattern between SAD and non-SAD patients (p ≤ 0.05). In SAD patients, upregulated proteins included paraoxonase-1 (PON1), thrombospondin 1 (THBS1), and full fibrinogen gamma chain (FGG), whereas downregulated proteins comprised immunoglobulin (IgHV3) and complement subcomponent (C1QC). Thus, plasma EVs of SAD patients show significant changes in the expression of distinct proteins involved in immune system regulation and blood coagulation as well as in lipid metabolism in this pilot study. They might be a potential indicator for to the pathogenesis of SAD and thus warrant further examination as potential biomarkers, but further research is needed to expand on these findings in longitudinal study designs with larger samples and comprehensive polymodal data collection.
To analyze the protein profile of human vitreous of untreated patients with retinal vein occlusion (RVO).
Sixty-eight vitreous humor (VH) samples (44 from patients with treatment naïve RVO, 24 ...controls with idiopathic floaters) were analyzed in this clinical-experimental study using capillary electrophoresis coupled to mass spectrometer and tandem mass spectrometry. To define potential candidate protein markers of RVO, proteomic analysis was performed on RVO patients (n = 30) and compared with controls (n = 16). To determine validity of potential biomarker candidates in RVO, receiver operating characteristic (ROC) was performed by using proteome data of independent RVO (n = 14) and control samples (n = 8).
Ninety-four different proteins (736 tryptic peptides) could be identified. Sixteen proteins were found to be significant when comparing RVO and control samples (P = 1.43E-05 to 4.48E-02). Five proteins (Clusterin, Complement C3, Ig lambda-like polypeptide 5 (IGLL5), Opticin and Vitronectin), remained significant after using correction for multiple testing. These five proteins were also detected significant when comparing subgroups of RVO (central RVO, hemi-central RVO, branch RVO) to controls. Using independent samples ROC-Area under the curve was determined proving the validity of the results: Clusterin 0.884, Complement C3 0.955, IGLL5 1.000, Opticin 0.741, Vitronectin 0.786. In addition, validation through ELISA measurements was performed.
The results of the study reveal that the proteomic composition of VH differed significantly between the patients with RVO and the controls. The proteins identified may serve as potential biomarkers for pathogenesis induced by RVO.
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