The document discusses carbohydrates and their roles in glycoproteins, glycolipids, and proteoglycans. It explains that carbohydrates are covalently attached to proteins or lipids through glycosylation to form these glycoconjugates. Glycosaminoglycans are linear polysaccharides that help form the extracellular matrix. Common examples discussed include hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparan sulfate, and keratan sulfate. Proteoglycans are core proteins with attached glycosaminoglycan chains that interact with extracellular proteins. Glycoproteins have oligosaccharide chains attached to asparagine or serine/threonine residues. Gly

1. Carbohydrate
Deependra Shrestha
M.Sc.Cli. Biochemistry
First Year
8th May 2016

2. Glycosylation
• The process in which carbohydrate compound is
covalently attached to the protein is called
glycosylation
• This type of molecule is called glycoprotein.
• Oligosaccharide may be attached to protein
• with the nitrogen atom of asparagine(called the N-
Linked)
• With the oxygen atom of threonine or serine(O-Linkage)
• The sites of glycosylation depends on the sequence
of amino acids surrounding asparagine, serine and
threonine.

3. • N acetylglucosamine is covalently attached to the
nitrogen of asparagine through N-linked
glycosylation.
N-Linked

4. The carbohydrate is attached at its anomeric carbon through a glycosidic link to the
–OH of serine or threonine residue

5. Glycosaminoglycans
• Glycosaminoglycans are extracellular heteropolysaccharide
which consist of linear polymer composed of repeating
diasaccharide unit .
• One of the two monosaccharides is always either N-
acetylglucosamine or N- acetylgalactosamine.
• other monosaccharide are Uronic acid i.e. D-glucuronic acid
or L-iduronic acid
• The combination of sulfate groups and carboxylated group of
uronic acid residue gives glycosaminoglycans which is a very
high electron density molecule.

6. Glycosaminoglycans
• the important component of ECM
• form a meshwork with fibrous proteins like
collagen, elastin, fibronectin etc
Hyaluronic acid
Heparin
Chondroitin sulfate
Dermatan sulfate

7. Hyaluronic acid:
• The Greek hyalos means “glass”; hyaluronan can have glassy
or translucent appearance
• contains alternating residues of D-glucuronic acid and N-
acetylglucosamine linked by (β1→4) and (β1→3) linkages
• 50, 000 repeats of the basic disaccharide unit
• High molecular weight of several million
• Present in connective tissues, cartilage, synovial fluid and
vitreous humor
• Hydrolyzed by Hyaluronidase present in
• some pathogenic bacteria
• sperm of many species of animal

8. Hyaluronan(hyaluronic acid)

9. Chondroitin Sulphate:
• Greek chondros, “cartilage”
• 20-60 repeated units of glucoronic acid and N-
acetylgalactosamine sulphate linked by (β1→3) and
(β1→4) linkage.
• Widely distributed in cartilage, tendons, ligaments, and
the wall of the aorta
• Contributes to the tensile strength of cartilage, tendon,
ligament and the walls of aorta.

10. Chondroitin Sulfate

11. Dermatan Sulphate:
• Greek derma, “skin”
• Found in skin, blood vessels and heart valves
• Repeated units of L-iduronic acid and N-
acetylgalactosamine in (β1→3) linkages

12. Keratan Sulphate:
• Greek keras, “horn”
• Does not contain uronic acid and sulfate content is variable
• Repeated units are galactose and N-acetylglucosamine in
beta linkage
• Found in cornea, tendons and variety of horny structures
formed of dead cells

13. Heparan sulphate:
• Greek hepar, “liver”
• Variable arrangement of sulfated and non sulfated sugar
• Repeated units of sulphated glucosamine and L-iduronic
acid by (α1→4) linkage
• Heparin is a fractionated form of heparan sulfate
derived mostly from mast cells
• In vivo, used as anticoagulant as it binds antithrombin
(activates antithrombin)
• The interaction is strongly electrostatic as it has the
highest negative charge density of any known biological
macromolecule

14. Heparin

15. Glycoconjugates
• Polysaccharides that serve as information carriers
communication between cells and their extracellular
surroundings
serve as recognition sites for extracellular signal molecule
Labelling of proteins for transport to specific organelles and
also destruction if protein is malformed or if overproduced
Recognition site for extracellular signal molecule
Cell to cell recognition and adhesions
• Biologically active molecule.

16. Glycoconjugates
• specific oligosaccharide chains attached to components of
the plasma membrane to form a carbohydrate layer which
is known as glycocalyx
• serves as an information-rich surface
• informational carbohydrate is covalently joined to a
protein or a lipid
• Types
Proteoglycans
Glycoprotein
Glycolipid

17. Proteoglycans

18. • consists of a "core protein" with one or more covalently
attached glycosaminoglycan chain(s). The point of attachment is a
Ser residue to which the glycosaminoglycan is joined through a
tetrasaccharide bridge

19. Proteoglycans
• Macromolecules of the extracellular matrix in which one
or more sulfated glycosaminoglycan chains are joined
covalently to the membrane protein or a secreted protein
• The glycosaminoglycan chain can bind to extracellular
proteins through electrostatic interaction with the
negatively charged groups on the polysaccharide
• Major component of ECM

20. Proteoglycans
• Many are secreted into the extracellular matrix, but some
are integral membrane proteins
• Eg. basal lamina, the sheet like ECM, contains a family of
core proteins, each with several covalently attached
heparan sulfate chains
• two major families of heparn sulfate proteoglycans:
• Syndecans
• Glypicans

21. Proteoglycans

22. Proteoglycans
• Syndecans: have single transmembrane domain and
an extracellular domain bearing 3-5 chains of
heparan or chondroitin sulfate
• Glypicans: are attached to membrane by a lipid
anchor (GPI anchor)
• Both of these can be shed into extracellular space in
the form of syndecan ectodomains and glypicans

23. Proteoglycans
Functions:
• can bind to a variety of extracellular ligands and thereby
modulate the ligand’s interaction with specific receptors
of the cell surface
Eg. Heparan sulphate
• demonstrate 2 structures: NS domain and NA domain
• NS domain - Highly sulfated domain
• NA domain - having unmodified GlcNAc and GlcA residues

24. Proteoglycans

25. Proteoglycans
• NS domains bind specifically to extracellular proteins and
signaling molecules to alter their activities
• change in activity may result from :
• a conformational change in the protein
• enhanced protein-protein interactions
• As a co-receptor for extracellular ligands
• Cell surface localization/concentration

26. Proteoglycans

27. Proteoglycans

28. Proteoglycans
Proteoglycan aggregate:
• enormous supramolecular assemblies of many core
proteins all bound to a single molecule of hyaluronan
• Aggrecan core protein has multiple chains of chondroitin
sulfate and keratan sulfate, joined to Serine residues in
the core protein through tetrasaccharide linkers, to give
an aggrecan monomer

29. Proteoglycans

30. Proteoglycans
• Fibrous matrix proteins such as collagen, elastin,
fibronectin are interwoven with EC proteoglycans to form
a meshwork which gives ECM strength and resilience
• The association between cells and the proteoglycan is
mediated by a memb. protein (integrin) and by an
extracellular protein (fibronectin)

32. Glycoproteins
• Glycoprotein have one or several oligosaccharides of
varying complexity joined covalently to produce protein
• 2 types of linkage between them
• O-linked with Ser, Thr residue
• N-linked with Asn residue
• the carbohydrate may constitute from 1% to 70% of
glycoprotein by mass

33. Glycoproteins

34. Glycoproteins
Eg.
• Mucin: secreted or membrane glycoproteins that
can contain large numbers of O-linked
oligosaccharide chains
• Glycophorin A
• Immunoglobulins
• FSH, LH, TSH

35. Glycoproteins
• advantages of adding oligosaccharides to proteins are
:
• hydrophilic clusters of carbohydrate alter the polarity and
solubility of the proteins
• Serves as destination labels and also act in protein quality
control, targeting misfolded proteins for degradation
• Oligosaccharide chains also protect some proteins from
attack by proteolytic enzymes.
• Oligosacharide chains are rich in information forming
highly specific sites for recognition and binding by carb.
binding proteins known as lectins

36. Glycolipids
• Are membrane sphingolipids having covalently bound
oligosaccharide (the hydrophilic head group exposed on
the outer surface of the cell)
Eg.
Gangliosides - are membrane lipids in which the polar
head group is a complex oligosaccharide containing a
sialic acid and other monosaccharide residues

37. Glycolipids
Lipopolysaccharides:
• Present in the outer membrane of Gram –ve
bacteria
• are prime targets of the antibodies and are
therefore important determinants of the serotype
of bacterial strains

38. Glycolipids

39. Glycomics
• systematic characterization of carbohydrate
components of a given cell or tissue, including those
attached to proteins and to lipids
• determining which proteins are glycosylated and
where in the amino acid sequence each
oligosaccharide is attached

40. Lectin
• proteins that bind carbohydrates with high
specificity and with moderate to high affinity
• serve in a wide variety of cell-cell recognition,
signaling and adhesion processes and in
intracellular targeting of newly synthesized proteins

41. Lectin
• Protein that binds carbohydrate with high specificity
and with moderate to high affinity.
• Some peptide hormones that circulate in the blood
have oligosaccharide moieties that strongly influence
their circulatory half-life
Eg.
Luteinizing hormone and thyrotropin
• have N-linked oligosaccharides that end with the
disaccharide GalNAc4S (β1→4) GlcNAc, which is
recognized by a lectin (receptor) of hepatocyte

42. Lectin
• Oligosaccharide chains of many plasma glycoproteins
protect those proteins from uptake and degradation
in the liver
Eg.
• ceruIoplasmin, a copper-containing serum
glycoprotein has several oligosaccharide chains
ending in Neu5Ac
• Plasma membrane of hepatocytes has lectin
molecules that specifically bind oligosaccharide
chains without Neu5Ac

43. Lectin
• receptor that recognizes hydrolytic enzymes
containing mannose-6-phosphate and targets these
proteins for delivery to the lysosomes.
• I-cell disease is one type of defect in this particular
system.

44. Lectin
• lectin of the influenza virus, known as the HA
(hemagglutinin) protein is essential for viral entry
and infection; oseltamivir and zanamivir
• Lectins on the surface of the HSV-I and HSV-2 bind
specifically to heparan sulfate on the host cell
surface as a first step in the infection cycle

45. Lectin
• microbial pathogens have lectins that mediate
bacterial adhesion to host cells or the entry of toxin
into cells
E.g. Helicobacter pylori
• adheres to the inner surface of the stomach as
bacterial membrane Iectins interact with specific
oligosaccharides of membrane glycoproteins of the
gastric epithelial cells

46. Lectin
Selectins :
• are a family of plasma membrane lectins that mediate
cell-cell recognition and adhesion in a wide range of
cellular processes
E.g.
• movement of immune cells (neutrophils) through the
capillary wall from blood to tissues, at sites of infection
or inflammation

47. Lectin
 Human selectins mediate the inflammatory responses
in RA, asthma, psoriasis, MS and the rejection of transplanted
organs

48. Thank you
•Reference
• Tietz textbook of Clinical chemistry And molecular
Diagnostics. 5th edition
• Lehninger Principles Of Biochemistry
• Lippincott’s illustrated reviews: Biochemistry
• Practical Manual of Biochemistry