Lehninger Principles of Biochemistry

Transcription

1 David L. Nelson and Michael M. Cox Lehninger Principles of Biochemistry Fourth Edition Chapter 7: Carbohydrates and Glycobiology Copyright 2004 by W. H. Freeman & Company

2 polyhydroxy aldehydes or ketones, or substances that yields such compounds on hydrolysis

3 Most abundant biomolecules By photosynthesis, 100 billion CO 2 & H 2 O cellulose and plant products (not all) empirical formula (CH 2 O) n Their Functions in livings A dietary staple Energy-yield pathway in non-plants Structural & protective element in cell wall of bacteria, plants and in connective tissue of animals Lubricant in skeletal joints Recognation & adhesion between cells Signals (L+C or L+P: glycoconjugates)

4 Types (size) Monosaccharides (monomer) Simple sugar A single polyhydroxy aldehyde or ketone unit Most abundant six-carbon sugar D-glucose (dextrose) Oligosaccharides (2-20 monomer) Disaccharides: 2 monomers Sucrose (abundant):d-glucose+d-fructose Not free, linked to other biomolecules in cell Polysaccharides (>20 monomer) Starch: chain Glycogen:branched Glycosidic linkage

5 Monosaccharides and Disaccharides Either aldehydes or ketones with two or more hydroxyl groups Colorless, soluble in water, crystalline Most sweet A carbonyl (aldehyde or ketone) group + many hydroxyl group Aldose: if carbonyl at the tip Ketose: if carbonyl at any other

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7 Monosaccharides and Disaccharides Simplest: 2-carbon trioses: Glyceraldehyde (an aldotriose) Dihydroxyacetone (a ketotriose) How to name MS acc. # of Carbon 3C triose 4C tetrose 5C pentose 6C hexose 7C heptose

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10 CH asymetric centers # of Chiral center: >1 Glyceraldehyde 1 chiral center # of stereoisomer= 2 n (n=# of chiral center) X-ray crystalography for 3D but Fisher projection formulas to represent them 3D on paper Stereoisomers of sugar can be L or D 6 C means 4 chiral C. So 2 4 =16 stereoisomers 8 D; 8 L

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14 How to define which one is D or L Find the carbonyl Carbon Find the farest carbon Compare with gyceraldehyde; if hydroxyl on left D; if not L

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16 Epimers: sugars configuratonal difference only one C atom

17 4-5 carbon ketoses ul into the corresponding aldose

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20 In aqueous solution:cyclic >4 carbon backbonded MS cyclic (ring) Carbonyl (aldehyde or ketone)--- O of hydroxyl of (mostly last) any C Aldehyde + alchol = hemiacetal Ketone + alcohol = hemiketals

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22 Two stereoisomers while cyclic α and β stereoisomers Six-membered ring pyranose Mutaration interconvertion of alfa to beta Five-membered furanose In normal aquoes soltion 1/3 α-d glucopyranose 2/3 β -D glucopyranose Very small linear and glucofuranose

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24 2 possible conformation (without bond breaking) 2 chair forms of 2 chair forms of pyranose rings

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26 Hexose Derivatives Bacterial cell wall Bacterial cell wall

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31 In animals as glycoconjugate

32 Reducing agent:monosaccharides carbonyl carboxyl Reducing sugars: sugars that reduce Fe 3+ (ferric) or Cu 2+ (cupric)

33 BUT TODAY WE USE A DIFFERENT METHOD

34 Disaccharides Glycosidic Bond DS =MS + O-glycosidic bond + MS Between anomeric carbon of one and hydroxyl of another glycosidic bond:easly hydrolyzed by acid but base Boil wth dilute acid monosaccharides

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36 Non-reducing end Why because it is not free. Reducing end Why because it is free.

37 How to name DS Glycosidic Look at first bond s one direction whether in it paranthesis α or β. In example, it is β Example: (1 4) Name-Nonreducing second residuend sugar; furano or pyrona If 3.residue write the bond

38 İn milk D enintomer and pyronose is common abbreviated nomenculator

39 In plant not by animals is nonreducing sugar It means no free anomeric carbon Double headed arrow

40 Circulating fluid (hemolymph) of insects, energy fuil

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42 Polysaccharides (glycans) Classification identity of their recurring MS Size Branch Types of bonds

43 Polysaccharides (glycans) Homopolysaccharides Single type of monomer Storage (glycogen, starch) Structural (chitin, cellulose) Heteropolysaccharides 2 or > types Extrocellular support

44 Homopolysaccharides as energy source Starch (plants) and Glycogen (animals) Both intracellular granules Heavily hydrated (many OH) Readly dissolved

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47 Starch Two types Amylose Amylopectin Amylose: Long, unbranched (α 1-4) linkages of D-glucose

48 Amylopectin Up to 100 million Dalton Branched (α 1-6) at branches One branch/(24-30 residues)

49 Many nonreducing end One reducing end

50 Glycogen Storage in animals (mostly liver; some skel) Like amylopectin but more branched (1/8-12 residue) More compact than starch Several million Degraded enzyme work from nonreducing end Q:Why glycogen? Why not all glucoses one by one? A: [glycogen]:0.01 µm but if it were degraded [glucose]: µm osmolarity

51 Bacterial and yeast PS Dextran (α1 6) linked poly-d-glucose Branched with (α1 3) in all, ((α1 2)& (α1 6) in some) Some sticky dextran by bacteria (streptococcus mutant) makes dental plaque Synthetic dextran in artifical blood Sephadex etc

52 Homopolysaccharides as structural 1. Cellulose roles 2. Chitin

53 1. Cellulose Fibrous, tough, water-insoluble in cell walls of plants (stems, trunks etc.) Cotton ~100% cellulose Linear, unbranched ( D-glucose units) Like amylose, amylopectin, glycogen Main difference β (β 1 4) α-amylase: enzyme breaking (α 1 4) amylose, starch, glycogen but not cellulose Cellulase: enzyme breaking (β 1 4) of cellulose Trichonympha Termites Wood-rot fungi and bacteria

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56 2. Chitin Linear with N-acetylglucosamine in β- linkage Exoskeloton of nearly a million species of arthropodsinsects, lobsters, crabs etc Most abondunt PS after cellulose in nature

57 Only difference betwen chitin and cellulose: Acetylated amine Cellulose

58 3D of PS Depends on interactions Hydrogen bonding Hydrophobic Van der-walls Electrostatic interaction (polymer with charged res.)

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64 Bacterial&Algal Cell Walls Heteropolysaccharides Cell wall against lysis Lysozyme degrade cell wall (β1-4)gylcosidic bond btwen them Tears Baacteral viruses

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67 Extracellular matrix: Glycosaminoglycans Heteropolsaccharides Gel-like Extracellular matrix: glycosaminoglycans + proteins Glycosaminoglycans: polymers of repeting disaccharides (monomer)

68 >1 million D Vitrous humor (liquid inside the eye ball) Component of extracellular matrix of tendons and cartilage

69 Other glycosaminglycans Shorter than hyaluronate Proteoglycans (linked to proteins)

70 Tensile strength of cartilage, tendons, ligaments, walls of aorta.

71 In cornea, cartilage, bone and a variety of horny structure (horn, hair etc)

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74 Glycoconjugates: Proteoglycans, Glycoproteins, Glycolipids Cell-cell recognation Cell-cell adhesion Cell migration during development Blood cloting İmmune response Wound healing

75 Glycoconjugates: charbohydrates + (lipid or protein) Proteoglycans: CH + membrane or secreted protein Glycosaiminoglycans moiety main part Major parts of connective tissue Glycoproteins: a few oligosacch. Outher surface of plasma membrane In extracellular matrix Blood İn cell (golgi, lysosomes, secretory granules) Their cahins specific, informative Glycolipids Membrane lipids attached oligosac.

76 Proteoglycans Glycosaminoglycan-coating macromolecules (30 members of the family) Cell surface (integral protein) Extracellular matrix Basal lamina: heparin sulfate chain + trisaccharide Basal lamina: heparin sulfate chain + trisaccharide bridge + core protein (20kD-40 kd)

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78 1 2 3

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84 Proteoglycan aggregates (~2000kD) =aggrecan core protein(250kd) +CS +KS Function:make the extracellular matrix strength (with collagen etc)

85 Multiple binding sites for matrix elements and ligands (signal) Multiple binding sites

86 Glycoproteins Protein + carbohydrate (its moiety small)

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88 Glycolipids and Lipopolysaccharides Membrabe components Glycolipids: Ganglioisedes (membrane lipid + CH) Blood groups Lipopolysaccharides Found on the surface of some bacteria Target for antibiotics Toxic Lower blood pressure

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90 CH as informative molecule CH more nformative than others 14 units : CH 1.44x10 15 NA: 4096 Peptide: 6.4x10 7 Lectin: proteins that bind CH with high affinity and specificity Function: Cell-cell recognation Signaling Adhesion process İntacelullar targeting of newly synthesized proteins

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92 Some hormones and RBC are marked with Oligos. Moiteies Funciton: affect their half-life: if you remove, half-life decrease Selectins: a family of plasma membrane lectins F: cell adhesion Cell-cell recognation

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94 Cholera toxin (vibrio cholera) oligosaccharide of GM1, ganglioside, of intestinal epithelial cells diarrhea

95 Lectins ~intracellular and highley specific for oligos. FIGURE 7 35 Details of lectincarbohydrate interaction. (a) X-ray crystallographic studies of a sialic acid specific lectin (derived from PDB ID 1QFO) show how a protein can recognize and bind to a sialic acid (Neu5Ac) residue. Sialoadhesin (also called siglec- 1), a membranebound lectin of the surface of mouse macrophages, has a sandwich domain (gray) that contains the Neu5Ac binding site (dark blue). Neu5Ac is shown as a stick structure.

96 (b) Each ring substituent unique to Neu5Ac is involved in the interaction between sugar and lectin: the acetyl group at C-5 has both hydrogen-bond and van der Waals interactions with the protein; the carboxyl group makes a salt bridge with Arg97; and the hydroxyls of the glycerol moiety hydrogen-bond with the protein

97 (c) Structure of the bovine mannose 6-phosphate receptor complexed with mannose 6- phosphate (PDB ID 1M6P). The protein is represented here as a surface contour image, with color to indicate the surface electrostatic potential: red, predominantly negative charge; blue, predominantly positive charge. Mannose 6-phosphate is shown as a stick structure; a manganese ion is shown in green.

98 Mannose 6-phosphate is hydrogen-bonded to Arg111 and coordinated with the manganese ion (green). The His105 hydrogen-bonded to a phosphate oxygen of mannose 6- phosphate may be the residue that, when protonated at low ph, causes the receptor to release mannose 6-phosphate into the lysosome.

99 Polar sidec of galactose with polar ones of protein and hydrophobic sides with indolyl moiety of Trp.

100 FIGURE 7 37 Roles of oligosacharides in recognition and adhesion at the cell surface.(a) Oligosaccharides with unique structures (represented as strings of hexagons), components of a variety of glycoproteins or glycolipids on the outer surface of plasma membranes, interact with high specificity and affinity with lectins in the extracellular milieu. (b) Viruses that infect animal cells, such as the influenza virus, bind to cell surface glycoproteins as the first step in infection. (c) Bacterial toxins, such as the cholera and pertussis toxins, bind to a surface glycolipid before entering a cell. (d) Some bacteria, such as H. pylori, adhere to and then colonize or infect animal cells. (e) Selectins (lectins) in the plasma membrane of certain cells mediate cellcell interactions, such as those of T lymphocytes with the endothelial cells of the capillary wall at an infection site. (f) The mannose 6-phosphate receptor/lectin of the trans Golgi complex binds to the oligosaccharide of lysosomal enzymes, targeting them for transfer into the lysosome.

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