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7: Carbohydrates and Glycobiology - Biology

7: Carbohydrates and Glycobiology - Biology


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7: Carbohydrates and Glycobiology

Glycobiology of human milk

Glycans are characteristic components of milk, and each species has unique patterns of specific carbohydrates. Human milk is unusually rich in glycans, with the major components being lactose and oligosaccharides, representing approximately 6.8 and 1% of the milk, respectively. Other sources of glycans in human milk include monosaccharides, mucins, glycosaminoglycans, glycoproteins, glycopeptides, and glycolipids. In human milk, the presence and patterns of these glycans vary depending upon the stage of lactation and the maternal genes and their genetic polymorphisms that control glycosyl transferases. The synthesis of milk glycans utilizes a significant portion of the metabolic energy that the mother expends when producing her milk, but other than lactose, these glycans contribute little to the nutritional needs of the infant. The data herein support several functions. 1) Many human milk glycans inhibit pathogens from binding to the intestinal mucosa. 2) Human milk glycans attenuate inflammation. 3) Glycans also directly stimulate the growth of beneficial (mutualist) bacteria of the microbiota (formerly considered commensal microflora of the intestine) these mutualists and their fermentation products can, in turn, (a) inhibit pathogens, (b) modulate signaling and inflammation, and (c) the fermentation products can be absorbed and utilized as a source of dietary calories. These functions can help direct and support intestinal postnatal growth, development, and ontogeny of colonization. The many functions of the milk glycans may synergistically protect infants from disease. Hence, human milk glycans and their homologs may serve as novel prophylactic or therapeutic agents for a diverse range of deleterious conditions.


Chapter 7 - Carbohydrates and Glycobiology

Carbohydrates: ● Formula → Cn(H2O)n ● Produced from CO2 and H2O by photosynthesis in plants ● Range from glyceraldehyde to amylopectin ● Can be covalently linked with proteins and lipids ● Nomenclature → number of carbon atoms in the carbohydrate + -ose ending ● Monosaccharides → one sugar unit ● Oligosaccharides → short chains of sugar units ● Polysaccharides → &gt20 sugar units ● All initially had a carbonyl functional group ● Aldose = aldehydes ● Ketose = ketones

Functions of Carbohydrates: ● Energy sources and energy storage ● Structural component of cell walls and exoskeletons ● Informational molecules in cell-cell signaling

Constitutional Isomers of Carbohydrates: ● Aldose is a carbohydrate with aldehyde functionality ● Ketose is a carbohydrate with ketone functionality

Stereoisomers of Carbohydrates: ● Enantiomers → mirror images of each other ● Epimers → differ in configuration around one carbon atom ● Stereoisomers → nonsuperimposable mirror images ● Number of stereoisomers = 2n (n is number of chiral centers) ● In sugars with many chiral centers, only the one that is most distant from the carbonyl carbon is designated as D (right) or L (left) ● D and L isomers of sugars are enantiomers (have samewater solubility) ● Most hexoses in living organisms are D stereoisomers ● Some single sugars occur in the L form (such as L-arabinose) ● Chiral carbons are usually represented by Fischer projections

Stereoisomers: ● Epimers are stereoisomers that differ at only one chiral center ● Epimers are not mirror images → Epimers are not enantiomers ● Epimers are diastereomers ● Diastereomers → have different physical properties (ex. Water solubility and melting temperature)

Diastereomers: ● Stereoisomers that are not mirror images ● Have different physical properties

Epimers: ● D-Mannose and D-galactose are both epimers of D-glucose ● D-Mannose and D-galactose vary at more than one chiral center and are diastereomers, but not epimers

Common Carbohydrates: ● Ribose → standard five-carbon sugar ● Glucose → standard six-carbon sugar ● Galactose → epimer of glucose ● Mannose → epimer of glucose ● Fructose → ketose form of glucose

Hemiacetals &amp Hemiketals

Cyclization of Monosaccharides: ● Nucleophilic alcohol attacks electrophilic carbonyl carbon, allowing formation of a hemiacetal ● As a result, the linear carbohydrate forms a ring structure ● At the completion of the structure, the carbonyl carbon is reduced to an alcohol ● Orientation of the alcohol around the carbon is variable and transient ● Pentoses and hexoses readily undergo intramolecular cyclization ● Former carbonyl carbon becomes a new chiral center - anomeric carbon ● When the former carbonyl oxygen becomes a hydroxyl group, the position of this group determines if the anomer is a or B ● If the hydroxyl group is on the opposite side (trans) of the ring as the CH2OH moiety, the configuration is a ● If the hydroxyl group is on the same side (cis) of the ring as the CH2OH moeity, the configuration is B

Cyclization of Monosaccharides

Cyclization of Monosaccharides - Pyranoses and Furanoses: ● Six membered oxygen-containing rings called pyranoses after the pyran ring structure ● Five membered oxygen-containing rings are called furanoses after the furan ring structure ● The anomeric carbon is usually drawn on the right side

Anomers and Mutarotation: ● a and B configurations are interconvertible by mutarotation ● Anomers - isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom

Glycosidic Bond: ● 2 sugar molecules can be joined by a glycosidic bond between an anomeric carbon and a hydroxyl carbon ● The glycosidic bond (an acetal) between monomers is more stable and less reactive than the hemiacetal at the second monomer ● The 2nd monomer, with the hemiacetal, is reducing ● The anomeric carbon involved in glycosidic linkage is nonreducing ● Disaccharides can be named by the organization and linkage or a common name ● Disaccharide is formed upon condensation of 2 glucose molecules by a 1 → 4 bond described as a-d-glucopyranosyl - (1 → 4) - d- glucopyranose ● Common name for disaccharide is maltose

Nonreducing Disaccharides: ● Can transform to -CHO and -OH → reducing end ● 2 sugar molecules can be joined by a glycosidic bond between 2 anomeric carbons ● The product has 2 acetal groups and no hemiacetals ● There are no reducing ends → non reducing sugar

Polysaccharides: ● Natural carbohydrates are usually found as polymers ● Polysaccharides can be homopolysaccharides (one monomer unit), heteropolysaccharides (multiple monomer units), linear (one type of glycosidic bond), or branched (multiple types of glycosidic bonds ● Polysaccharides do not have a defined molecular weight ● No template is used to make polysaccharides → unlike proteins ● Often in a state of flux → monomer units are added and removed as needed by the organism

Homopolysaccharides &amp Heteropolysaccharides

Glycogen: ● Homopolymer of glucose ● Glycogen is a branched homopolysaccharide of glucose ● Glucose monomers form (a1 → 4) linked chains ● There are branch points with (a1 → 6) linkers every 8-12 residues ● Functions as the main storage polysaccharide in animals

Starch: ● Mixture of 2 homopolysaccharides of glucose ● Amylose → unbranched polymer of (a1 → 4) linked residues ● Amylopectin → branched like glycogen, but the branch points with (a1 → 6) linkers occur every 24-30 residues ● Starch is the main storage polysaccharide in plants

● Water insoluble ● Found in cell walls in mushrooms and in exoskeletons of insects, spiders, crabs, and other arthropods

Agar and Agarose: ● Agar is a branched heteropolysaccharide composed of agarose and agaropectin ● Agar serves as a component of cell wall in some seaweeds ● Agar solutions form gels that are commonly used in the laboratory as a surface for growing bacteria ● Agarose solutions form gels that are used for separation of DNA by electrophoresis

Glycosaminoglycans: ● Linear polymers of repeating disaccharide units ● One monomer is either N-acetyl-glucosamine or N-acetyl-galactossamine ● Negatively charged → uronic acids (C6 oxidation) and sulfate esters ● Extended hydrated molecule minimizes charge repulsion ● Forms meshwork with fibrous proteins to form extracellular matrix → connective tissue and lubrication of joints

Glycosaminoglycan &amp Heparin

Heparin and Heparan Sulfate: ● Heparin is a linear polymer ● Heparan sulfate is a heparin-like polysaccharide attachedto proteins ● Highest negative-charge density biomolecules ● Prevents blood clotting by activating protease inhibitor antithrombin ● Binding to various cells regulates development and formation of blood vessels ● Can also bind to viruses and bacteria and decrease their virulence ● Heparin is only produced by mast cells and functions an an anticoagulant ● Heparan sulfate (HS) is made by almost all cell types and has some anticoagulant activity ● Binding sites for heparan sulfate is rich in Arg and Lys residues ● Molecular basis for heparan sulfate enhancement of the binding of thrombin to antithrombin ● Thrombin is an enzyme in blood plasma that causes the clotting of blood by converting fibrinogen to fibrin

Glycoconjugates - Glycoprotein: ● Protein with small oligosaccharides attached ● Carbohydrate is attached by its anomeric carbon to amino acids on the protein ● Common connections occur at Ser, Thr, and Asn ● About half of mammal proteins are glycoproteins ● Only some bacteria glycosylate a few of their proteins ● Carbohydrates play roles in protein-protein recognition ● Viral proteins are heavily glycosylated → helps evade the immune system

Glycoconjugates - Proteoglycans: ● Sulfated glycosaminoglycans attached to large rod-shaped protein in cell membrane ● Syndecans → protein has a single transmembrane domain ● Glypicans → protein is anchored to a lipid membrane ● Interact with a variety of receptors from neighboring cells and regulate cell growth ● Proteoglycan is a protein bonded to glycosaminoglycan group, seen frequently in connective tissue

Heparan Sulfate NS Domain → Regions rich in sulfated sugars NA Domain → Regions with chiefly unmodified residues of GlcNAc and GlcA

Proteoglycans: ● Different glycosaminoglycans are linked to the core protein ● Linkage from anomeric carbon of xylose to serine hydroxyl ● Our tissues have many different core proteins → aggrecan is best studied

Proteoglycan Aggregates: ● Hyaluronana and aggrecan form huge noncovalent aggregates ● They hold a lot of water (1,000x its weight) and provide lubrication ● Low friction material ● Covers joint surfaces → articular cartilage ● Reduces friction and load balancing


Chemistry 501 Handout 7 Carbohydrates and Glycobiology Chapter 7 - PowerPoint PPT Presentation

Dep. of Chemistry & Biochemistry Prof. Indig Chemistry 501 Handout 7 Carbohydrates and Glycobiology Chapter 7 Lehninger. Principles of Biochemistry. &ndash PowerPoint PPT presentation

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Chapter 7 Carbohydrates and Glycobiology - PowerPoint PPT Presentation

PowerShow.com is a leading presentation/slideshow sharing website. Whether your application is business, how-to, education, medicine, school, church, sales, marketing, online training or just for fun, PowerShow.com is a great resource. And, best of all, most of its cool features are free and easy to use.

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For a small fee you can get the industry's best online privacy or publicly promote your presentations and slide shows with top rankings. But aside from that it's free. We'll even convert your presentations and slide shows into the universal Flash format with all their original multimedia glory, including animation, 2D and 3D transition effects, embedded music or other audio, or even video embedded in slides. All for free. Most of the presentations and slideshows on PowerShow.com are free to view, many are even free to download. (You can choose whether to allow people to download your original PowerPoint presentations and photo slideshows for a fee or free or not at all.) Check out PowerShow.com today - for FREE. There is truly something for everyone!

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Carbohydrates and Their Derivatives Including Tannins, Cellulose, and Related Lignings

3.01.1 Introduction

The fields of glycochemistry and glycobiology now feature prominently as mature disciplines. Indeed, the world of carbohydrates and associated natural products appears to have come into its own. 1–4 The diversity of structures made possible by Nature’s carbohydrate building set is greater than that of oligonucleotides or oligopeptides, 5 and has given carbohydrates pivotal roles in different areas of biology and chemistry. These range from interacting systems in embryonic development and the control of cell adhesion and cell activation to the provision of energy sources and structural platforms. The rapid development of more sensitive physical methods and analytical techniques 6,7 has led to significant advances in the understanding of the structure, dynamics, and biological functions of carbohydrates. Thus, NMR spectroscopic techniques have evolved to the point that subtle events can now be probed, e.g. the role of structure and dynamics in the binding of oligosaccharides to complementary receptors, 8–10 or the changes in pKas of catalytic groups during enzyme action. 11 Significantly, the advent of nanoprobe techniques has opened up new frontiers for the analysis of microgram quantities of complex carbohydrates. 12 Mass spectrometric analysis of carbohydrate-containing macromolecules has undergone a revolution with matrix-assisted laser desorption/time of flight and electrospray ionization techniques, 6,7 and high-performance capillary electrophoresis techniques are now used to probe cellular glycosylation events, with the ultimate goal of single-cell analysis. 13 Structural information derived from X-ray crystallography is now used to infer molecular mechanism, as in the translocation of sugars across a membrane by a transport protein 14 or the formation of a distorted sugar ring or covalent intermediate in a retaining glycosidase reaction. 11 Chemical and enzymatic 15 synthetic methodology now provides key compounds with which to probe the role of oligosaccharide-mediated or oligosaccharide-triggered biological events. A noteworthy contribution is the synthesis of a pentasaccharide related to heparin that stimulates the antithrombin III-mediated inhibition of blood coagulation factor Xa more effectively than the natural pentasaccharide ligand. 16 The emergence of several modern textbooks in the area of carbohydrate chemistry attests to the rapid advances in the synthetic field. 17–24

The advances described above have been matched by impressive developments in the field of molecular biology and the application of molecular biological techniques to problems in structural biology. The tools have been exploited very effectively in biosynthetic studies of carbohydrates and their derivatives. Indeed, the combination of classical and modern biosynthetic probes has opened up new vistas in the fields of glycobiology and glycochemistry. A logical, unifying theme that links the diverse types of carbohydrates is one of biosynthesis. Knowledge of biosynthetic pathways can be used to advantage in the treatment of disease, the engineering of desirable properties in carbohydrate-processing enzymes or carbohydrate polymers, and the design of carbohydrate-based therapeutics, immunodiagnostics, and vaccines. Accordingly, this volume presents the different aspects of carbohydrates and associated natural products along biosynthetic principles. Although the biological activities of the compounds are an important aspect of their chemical interest, priority has not been given to this subject. Similarly, aspects of isolation, structure elucidation, and synthesis have not been surveyed, although synthesis and structural aspects that relate to biosynthesis have been included in certain cases. The reader is referred to books on carbohydrate chemistry 3,4,17–24 for leading references in the synthetic areas not surveyed in this volume.


Institut für Molekulare Pharmazie, Universität Basel, Klingenbergstrasse 50, 4051 Basel, Switzerland

Dept. of Biological Chemistry, Johns Hopkins University School of Medicine, 725 N. Wolf St. Rm., 401 Hunterian Baltimore, MD 21205-2185, USA

Dept. de Chimie, URA 1686, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France

Institut für Molekulare Pharmazie, Universität Basel, Klingenbergstrasse 50, 4051 Basel, Switzerland

Dept. of Biological Chemistry, Johns Hopkins University School of Medicine, 725 N. Wolf St. Rm., 401 Hunterian Baltimore, MD 21205-2185, USA

Dept. de Chimie, URA 1686, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris Cedex 05, France

Summary

The Repertoire of N-Glycans on the Envelope Glycoprotein of HIV of Human Immunodeficiency Virus Produced in Different Cell Types

Evidence for the Occurrence of O-Glycans on the Envelope Glycoproteins of HIV-1 Produced in Certain Cell Lines

Oligosaccharides of gp 120 and gp 41 at N-Glycosylation Sites and Their Possible Influence on Viral Infectivity

gp 120 Glycosylation Can Influence Antigenicity and Immunogenicity

Saccharides Recognized by Carbohydrate-binding Proteins and Antibodies as Potential Neutralization Epitopes on the Envelope Glycoprotein of HIV-1


Watch the video: Monosaccharides - Glucose, Fructose, Galactose, u0026 Ribose - Carbohydrates (October 2022).