Biological Sciences
Glycocalyx
Glycocalyx is a layer of carbohydrates that coats the surface of cells. It plays a crucial role in cell recognition, adhesion, and protection. The glycocalyx is involved in various biological processes, including immune response, cell signaling, and pathogen recognition.
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10 Key excerpts on "Glycocalyx"
eBook - ePubMechanobiology
Exploitation for Medical Benefit
- Simon C. F. Rawlinson(Author)
- 2017(Publication Date)
- Wiley-Blackwell(Publisher)
3 Sugar‐Coating the Cell : The Role of the Glycocalyx in MechanobiologyStefania Marcotti and Gwendolen C. ReillyDepartment of Materials Science and Engineering, INSIGNEO Institute for In Silico Medicine, Sheffield, UK3.1 What is the Glycocalyx?
The cell coat or Glycocalyx is a proteoglycan‐rich layer on the external surface of the cell membrane. Its thickness and proteoglycan composition vary according to the cell type and function. Glycocalyx means “sugar cup,” and as well as long proteoglycan chains, it consists of small glycoproteins and glycosylated proteins, such that it contains a dense layer of glycosaminoglycan (GAG) chains (Tarbell and Pahakis 2006). This layer is also known as the pericellular matrix (PCM), though that term is more commonly used for the thick proteoglycan layer around chondrocytes forming the chondron, to distinguish it from the extracellular matrix (ECM), which forms the bulk cartilage. The terms “Glycocalyx” and “PCM” are often used interchangeably, but the chondrocyte PCM is particularly thick and is characterized by specific composition and features; it is reviewed in detail elsewhere (Guilak et al. 2006; Wilusz et al. 2014). In this chapter, we will not consider the chondrocyte PCM in detail, but will focus on the Glycocalyx of endothelial, bone, and muscle cells.The Glycocalyx components can be connected to the cell membrane via transmembrane proteoglycan‐binding proteins or can span through the phospholipidic double layer. Glycoproteins and proteoglycans have a strong negative charge and attract water, so the Glycocalyx is broadly very soft and water‐saturated. Its gel‐like characteristics modulate adhesion by providing resistance to certain protein–protein adhesions and enabling weak binding to specific molecules. To allow protein–protein binding, such as that between integrins and the ECM molecule fibronectin (Paszek et al. 2014), an energy barrier has to be overcome, with the proteoglycan molecules pushed aside or squashed to allow contact (Rutishauser et al. 1988; Soler et al. 1997, 1998; Sabri et al. 2000; Lipowsky 2012).
eBook - PDF- Peter Grunwald(Author)
- 2011(Publication Date)
- Jenny Stanford Publishing(Publisher)
Chapter 3 OLIGOSACCHARIDES AND GLYCOCONJUGATES IN RECOGNITION PROCESSES Thisbe K. Lindhorst Otto Diels Institute of Organic Chemistry, Christiana Albertina University of Kiel, Otto-Hahn-Platz 3/4, D-24098 Kiel, Germany [email protected] 3.1 INTRODUCTION All cells, eukaryotic cells in particular, are covered with carbohydrates of enormous diversity. These are part of different glycoconjugates, which are embedded into the lipid bilayer of the plasma membrane or associated to the Glycocalyx of the cell. The Glycocalyx is a highly complex sugar coating, which is typical and important for every eukaryotic cell. It can be considered to form an interconnecting supramolecular entity between the extracellular matrix and the cytoskeleton and, apparently, is an indispensable “cell organelle.” Saccharides are major constituents of the Glycocalyx, playing an essential role in cell biology. This is well-known for the famous blood group antigens of red blood cells, all of them being carbohydrates. The biological significance of cell surface carbohydrates in cell communication unfolds in a highly complex interplay with other Carbohydrate-Modifying Biocatalysts Edited by Peter Grunwald Copyright © 2012 Pan Stanford Publishing Pte. Ltd. www.panstanford.com 120 Oligosaccharides and Glycoconjugates in Recognition Processes molecules, both membrane-anchored receptors and soluble molecules. There are secreted or membrane-bound proteins, which can recognize carbohydrates to form carbohydrate–protein complexes that are involved in cell development, the immune system, signal transduction, and also states of disease and malignancy. These proteins are called the lectins and occur ubiquitously in all organisms. Intracellular lectins frequently recognize core structures from glycoconjugate oligosaccharides, while cell surface and extracellular lectins often bind to terminal carbohydrate residues.
eBook - PDFCell Surface and Extracellular Glycoconjugates
Structure and Function
- Robert P. Mecham(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Carbohydrates of glycoproteins have the structural complexity to act as informational molecules. Just a few monosaccharide units can generate a bewildering array of oligosaccharide structures. These highly complex carbohydrate structures arise due to the variations in the linkage positions and anomeric configurations of monosaccharides. Different branching patterns within the oligosaccharide side chains and their potential to carry various charged substituents such as sul-fates, phosphates, and other groups further complicate the structure of the carbohydrates of glycoproteins. The diverse oligosaccharide struc-tures on the cell surface participate in the regulation of cell growth and differentiation during embryogenesis and oncogenesis (Feizi, 1987). Several tumor-associated carbohydrate antigens have been described recently (Hakomori, 1991). In vitro studies have shown that alterations in cell surface carbohydrates affect the invasion process (Schallier et al., 1988). Tumor cell invasion has been correlated with a gradient in the level of sialylation (Schallier et al., 1988), although sialic acid itself has been reported to have a negative influence on the adhesive forces between cells, as mediated by CAMs (Brackenbury, 1985). Dennis et al. (1987) have reported that the expression of the metastatic pheno-type of certain tumor cell lines is directly related to cell surface carbohy-drates. In a recent study, Miyake and Hakomori (1991) have demon-strated the inhibition of metastatic deposition of a highly metastatic variant of mouse melanoma cells using monoclonal antibodies that specifically recognize the disaccharide structure Fucal-lGal/31-R; the structures of the R group itself had no effect. These studies and others emphasize the potential role of carbohydrates in the metastatic process of cells. B. Lectin Receptors The importance of lectins has been highlighted by various investiga-tors (Sharon and Lis, 1989).
eBook - PDFCarbohydrate Chemistry
Volume 37
- Amelia Pilar Rauter, Thisbe Lindhorst(Authors)
- 2011(Publication Date)
- Royal Society of Chemistry(Publisher)
The focus of this chapter is to give an insight into the biological significance of the serum N -glycome, highlighting some specific examples of glycobiomarkers in health and disease and exploring the increasingly clear connection between altered N -glycosylation in inflammation and cancer. We will particularly focus on N -linked glycans and discuss the exciting possibility of moving from discovery to clinical phase, where these changes might help to improve diagnostic and prognostic tools. 1. Introduction Considering that glycans are ubiquitously present on all cell surfaces, the fact that several human diseases involve disturbed glycan processing pathways comes as no surprise to the emerging field of Glycobiology. Alterations in cellular signalling pathways (either caused by disease specific mutations or by changes in the cellular milleu) can significantly affect the systems which underpin glycosylation, a complex and non-template-driven process. Glycans constitute the most abundant and diverse of the post-translational modifications: all cell surface and secreted glycoproteins must travel through the endoplasmic reticulum and the Golgi compart-ments, where addition of carbohydrates take place. Proteins which contain appropriate sequences can potentially acquire N -linked oligosaccharides (in sequons Asn-Xaa-Ser/Thr, where Xaa is any amino acid except Proline, Figure 1) or O -linked oligosaccharides (which can be found linked to Ser/ Thr). The structure and nature of the glycans strongly influence various National Institute for Bioprocessing Research and Training, Dublin-Oxford Glycobiology Laboratory, Fosters Avenue, Mount Merrion, Blackrock, Co. Dublin, Ireland Carbohydr. Chem. , 2012, 37, 57–93 | 57 functional aspects of glycoproteins such as cellular localization, turnover, protein quality control, and ligand–ligand interactions.
eBook - PDFCarbohydrate Chemistry
Chemical and Biological Approaches Volume 44
- Amélia Pilar Rauter, Thisbe K Lindhorst, Yves Queneau(Authors)
- 2020(Publication Date)
- Royal Society of Chemistry(Publisher)
Exploring the fascinating world of sialoglycans in the interplay with Siglecs Cristina Di Carluccio, a, y Rosa Ester Forgione, a, y Antonio Molinaro, a Paul R. Crocker, b Roberta Marchetti* a and Alba Silipo* a DOI: 10.1039/9781788013864-00031 The great relevance of glycans is observable by their molecular and structural hetero-geneity that translates into a multiplicity of biological processes which they are involved in. Understanding the role of glycans and glycosylation in immunity is critical to comprehend the etiology and the progression of relevant immune diseases. Siglecs (sialic acid-binding immunoglobulin-like lectins) group a broad range of cell surface immunomodulatory receptors that selectively recognize sialylated glycans, acting as regulators of immune system triggering tolerogenic or immunogenic responses. Here, we provide an overview of the interplay occurring between Siglecs and endogenous as well as exogenous pathogen-derived sialylated glycans, with the final aim of demonstrating the importance of Siglecs–sialoglycan axis in the therapeutic treatment of human diseases. 1 The biological importance of glycans Nearly all mammalian cell surfaces are covered by a complex, highly-hydrated gel-like matrix, the Glycocalyx, that is built up by a dense layer of complex glycoconjugates (glycolipids and glycoproteins). 1 Glycans are characterized by a huge degree of complexity due to the many combin-ations in which the composing monosaccharides can be arranged. Indeed, differently from the simple linear assembly of building blocks forming proteins and nucleic acids, in the enzyme-regulated glycosyla-tion process the monomeric units structuring glycans can vary in terms of linkage position, anomeric configuration, ring size, substitution patterns, can be linear or branched, can be bound to proteins or lipids, can adopt different shapes.
eBook - PDF- Hans Neurath(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
This carbohydrate-specific interaction appears to be me-diated by a mannose-specific lectin present on the surface of the bac-teria (Ofek et al, 1977, 1978; Bar-Shavit et al., 1977; Eshdat et al, 1978). Similarly, recognition of L-fucose by Vibrio cholera may be re-sponsible for the attachment of this bacterium to animal cells, which is probably mediated by a lectin specific for L-fucose on the bacterial surface (Jones and Freter, 1976). Attempts have been made to study the role of carbohydrates in in-tercellular adhesion with the aid of sugar derivatized beads. Chicken hepatocytes (Schnaar et al., 1978) and rat hepatocytes (Weigel et al., 1978) bound specifically to polyacrylamide gels to which N-acetylglu-cosamine or galactose, respectively, were chemically attached. The cell ligands involved in these interactions are not known, but in the case of the chicken hepatocytes, they may be related or identical to the chicken liver-binding protein responsible for the clearance of glyco-proteins from the circulating system (Lunney and Ashwell, 1976; see also p. 108). It would thus appear that in many systems recognition is based on the interaction between cell surface carbohydrates and lectins on ap-posing cells. An earlier suggestion (Roseman, 1970) that the recogni-tion is mediated by glycosyltransferases seems less likely, not the least because the evidence for the presence of these enzymes on cell surfaces is inconclusive (Keenan and Morre, 1975; Riordan and Forstner, 1978). VII. CONCLUDING REMARKS From the foregoing account it is clear that enormous progress has been made in our knowledge of the chemistry and biology of glyco-proteins. Not surprisingly, however, the new findings have led to new questions. Of particular interest are the questions regarding the bio-synthesis and function of glycoproteins.
eBook - PDF- J. Montreuil, J.F.G. Vliegenthart, H. Schachter(Authors)
- 1995(Publication Date)
- Elsevier Science(Publisher)
This prediction is now realized on the basis of the two new concepts of glycobiology and glycobiotechnology. However, we must recognize that it is often difficult to convince the public or private institutions of the importance of research on glycocon- jugates. In fact, in spite of the fascinating discoveries achieved in the field of glycan primary and three-dimensional structure, in many cases the real role of biological glycoconjugate glycans is still unknown and, in many cases, we are unable to answer the question: “Why are proteins and lipids glycosylated?”. On the whole, the role of many glycans remains obscure and the subject of speculation or controversy. As pointed out by Albert Neuberger in 1974 [26]: “We are now faced with the major problem of the biological function of the glycoproteins: in other words, we are asking the question how the activity of a protein, whatever it may be, is modified or fine-tuned by the presence of sugar residues”. However, we can be optimistic about the future and the progress of research in the domain of glycoconjugates in general, and of glycoproteins in particular, since the basis of the molecular biology of these compounds is now firmly established. Interest in these compounds is growing, partly due to impressive developments in the field of biotech- nology. A series of crucial discoveries have pointed to the following biological roles of glycans: (i) They intervene in the folding of proteins during their biosynthesis and favour their secretion out of the cell. (ii) They stabilize the conformation of proteins in a biologically active form thanks to glycan-glycan or glycan-protein interactions. (iii) They control the proteolysis of protein precursors leading to active proteins or peptides. (iv) They protect polypeptide chains against proteolytic attack by acting as shields. 3 (v) By the same protective mechanism, glycans mask peptide epitopes and cause the weak antigenicity of glycoproteins.
eBook - PDFThe Plasma Proteins
Structure, Function, and Genetic Control
- Frank W Putnam(Author)
- 2013(Publication Date)
- Academic Press(Publisher)
Such processes include cell rec-ognition, cell adhesion, contact inhibition, and growth regulation (Cook and Stoddart, 1973). Mucus glycoproteins consist of polypeptide chains to which are at-tached large numbers of oligosaccharide units that surround and shield 1 * indicates carbohydrate attachment. Rabbit IgG IgAl Zuc Lys-Pro-Thr*-Cys-Pro Thr-Pro-Ser*-Pro-Ser Gly-Gly-Ser*-Ser-Glu 200 John R. Clamp the protein core. The carbohydrate, therefore, must be the most impor-tant component in determining the physical, chemical, and biological properties of the molecules. Plasma glycoproteins provide much more of a problem when attempts are made to assess the significance of the carbohydrate content and indeed to decide whether the carbohydrate has any function at all. For most glycoproteins that have some activity that is easily measured, such as enzymes, the presence or absence or modification of the oligosac-charide units usually has no effect on the activity, for example, in the two forms of ribonuclease (Plummer and Hirs, 1963, 1964). In a few cases, however, removal of some carbohydrate does appear to have an effect. Certain rabbit antibodies, but not all, lose complement-fixing and opsonic activities when the IgG is treated with an endoglycosidase (Williams et ai, 1973). There are also a number of examples where the removal of sialic acid has an apparent effect upon the biological proper-ties of the glycoprotein and this effect will be discussed later. Neverthe-less, it would still be correct to state that in the majority of plasma glycoproteins, the role, if any, of the carbohydrate is still unknown. It would certainly be energetically favorable to the cell to dispense with the mechanisms necessary for glycoprotein biosynthesis, and the fact that this type of molecule exists at all is a strong indication that the oligosaccharide units are biologically functional.
- Brett Blackman, Tzung K Hsiai, Hanjoong Jo(Authors)
- 2010(Publication Date)
- World Scientific(Publisher)
M., Spaan, J. A., Rolf, T. M., and Vink, H. (2006) Atherogenic region and diet diminish Glycocalyx dimension and increase intima-to-media ratios at murine carotid artery bifurcation. Am J Physiol Heart Circ Physiol 290 (2), H915–920. 8. Nieuwdorp, M., van Haeften, T. W., Gouverneur, M. C., Mooij, H. L., van Lieshout, M. H., Levi, M., Meijers, J. C., Holleman, F., Hoekstra, J. B., Vink, H., Kastelein, J. J., and Stroes, E. S. (2006) Loss of endothelial Glycocalyx during acute hyperglycemia coincides with endothelial dysfunction and coagulation activation in vivo. Diabetes 55 (2), 480–486. 9. van den Berg, B. M., Nieuwdorp, M., Stroes, E. S., and Vink, H. (2006) Glycocalyx and endothelial (dys) function: from mice to men. Pharmacol Rep 58 (Suppl), 75–80. 10. Gouverneur, M., Berg, B., Nieuwdorp, M., Stroes, E., and Vink, H. (2006) Vasculoprotective properties of the endothelial Glycocalyx: effects of fluid shear stress. J Intern Med 259 (4), 393–400. 11. Pries, A. R., Secomb, T. W., and Gaehtgens, P. (2000) The endothelial surface layer. Pflugers Arch 440 (5), 653–666. 12. Tarbell, J. M., and Pahakis, M. Y. (2006) Mechanotransduction and the Glycocalyx. J Intern Med 259 (4), 339–350. 13. Weinbaum, S., Tarbell, J. M., and Damiano, E. R. (2007) The structure and function of the endothelial Glycocalyx layer. Annu Rev Biomed Eng 9 , 121–167. 14. Adamson, R. H., and Clough, G. (1992) Plasma proteins modify the endothelial cell Glycocalyx of frog mesenteric microvessels. J Physiol 445 , 473–486. 15. Bernfield, M., Gotte, M., Park, P. W., Reizes, O., Fitzgerald, M. L., Lincecum, J., and Zako, M. (1999) Functions of cell surface heparan sulfate proteoglycans. Annu Rev Biochem 68 , 729–777. 16. Osterloh, K., Ewert, U., and Pries, A. R. (2002) Interaction of albumin with the endothelial cell surface. Am J Physiol Heart Circ Physiol 283 (1), H398–405. Glycocalyx Structure and Role in Mechanotransduction 89 17.
eBook - PDF- Edward Bittar(Author)
- 1996(Publication Date)
- Elsevier Science(Publisher)
glycolipids (Hakomori, 1986) are integrated into the cell membrane and, still further glycoproteins of approximately 20- 200 kDa are secreted into the serum; for some proteins, the 268 ELIZABETH F. HOUNSELL NeuAc Fuc /NeuAc ~2-3/6 al-3 ~2-6 I I GalBI-3/4GIcNAcBI-2/4/6Man~I Fuc~ I +Gicl~cB 1-4ManB 1-4Gicl~cB 1- 4Gicl~cB 1-Asn GalSl-3/4Glcl~cgl-2/4/6Man~l/3 I I NeuAc Fuc /NeuAc a2-3/6 al-3 eu2-6 Polvlactosamine backbone GalB I-4GIcNAcB i- 3GalB I-4GIcNAcB i- 3/6GalB i- Figure 2. Generalized N-linked oligosaccharide chain to which are attached periph- eral-chain terminating sequences, for example those expressing the blood group and related antigens on single o~ repeating lactosamine-type sequences. (continued) transmembrane signal sequence is removed and they are transferred to membrane bound, lipid-linked anchors via an inositol phosphate-GlcNH2-glycan-Man-6- phosphate-ethanolamine (glycophosphatidyl-inositol) bridge attached to the amino acid carboxy-terminus of the protein (Thomas et al., 1990; Ferguson, 1991); outside the cell, proteoglycans and glycoproteins can be sequestered to the extracellular matrix, or passed into the blood stream; mucins largely take up their positions lining the respiratory and gastro-intestinal tracts. In each of these different scenarios, the oligosaccharides can have various effects on the underlying protein and oligosaccharide sequences themselves can be impor- tant as antigens and molecular recognition signals. The first area where the importance of human oligosaccharide sequences became apparent was in blood transfusion. The erythrocyte carries on its cell surface, glycoproteins and gly- colipids bearing the oligosaccharide antigens synthesized using the glycosyltran- ferases encoded by the blood group genes.
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