Polysachharides Glycoconjugates Lectins

1. CARBOHYDRATES II
DR. MANOJ ACHARYA
JUNIOR RESIDENT (1st YEAR)
DEPARTMENT OF BIOCHEMISTRY
BPKIHS

2. CONTENTS
▸ POLYSACCHARIDES
▸ GLYCOCONJUGATES
▸ LECTINS
.
2

3. ▸ Hermann Emil Louis Fischer – German biochemist who discovered Fischer esterification.
▸ Walter Norman Haworth - won nobel prize in 1937 for his investigations on carbohydrate
3

4. POLYSACCHARIDE
▸ Large polymeric oligosaccharides, formed by the glycosidic
linkages of multiple monosaccharides or their derivatives
▸ Plays vital role in storage and in maintaining structural
integrity.
▸ Linked- linear or branched fashion
4

5. POLYSACCHARIDE
.
Homopolysaccharides
Contain only a single
monomeric species. eg.
Glucosans, fructosans
Heteropolysaccharides
Contains two or more
different kinds, eg. GAGs
5

6. Homopolysaccharides
▸ Storage ‒ Starch (in plants),
Glycogen (in animals).
▸ Structural elements ‒ Cellulose (plants cell wall),
Chitin (animal exoskeleton).
6

7. Starch (Storage Homopolysachharide)
▸ Homopolymer composed of D-glucose unit held by α-
glycosidic bonds
Two polysachharides units of glucose
▸ 1. Amylose (15-20%)
▸ 2. Amylopectin(80-85%)
.
7

8. 1)Amylose:-
▸ Long unbranched chain with helical structure.
▸ 250-300 D-glucose unit held by α (1-4)glycosidic linkages
2) Amylopectin:-
▸ Branched chain with α (1-6)glycosidic bonds at the branching
points and α (1-4)linkages everywhere else.
▸ Branching is at every 24-30 glucose residues.
8

9. 9

10. Amylose Amylopectin
Structure-unbranched Structure-highly branched
259 to 300 D-glucose units linked
by α(1-4)linkages
Units joined together by alpha 1-4
linkages and at branch point with alpha
1-6 glycosidic linkage
Gives blue color with dilute iodine
solution
Gives red color with iodine solution
Occurs at the extent of 15 to 20%
and molecular weight is across
60,000
Occurs at 80 to 85% and molecular
weight is approx 5,00,000
Can be hydrolyzed with amylase
enzymes completely
Cannot be hydrolyzed with enzymes
completely
10

11. Glycogen
▸ Main storage polysaccharide of animal cells
▸ Also known as animal starch
▸ Most abundant in liver and also found in skeletal muscle
▸ Contain both α(1,4)links and α(1,6)branches at every 8 to 12
glucose unit
▸ It serve as a buffer to maintain blood glucose level
11

12. 12

13. Dextran
▸ are bacterial and yeast polysaccharides
▸ made up of (α1→6) linked poly-D-glucose and branches by (α 1→ 3) linkage
▸ Some also have (α 1→ 2) or (α 1→ 4) branches
▸ Molecular weight:40,000Da ;70,000 Da;75,000 Da
▸ Used as antithrombotic, to reduce blood viscosity, and as a volume expander
in anemia.
▸ Components of dental plaques.
13

14. Inulin
▸ Polysaccharide of fructose (fructosan)
▸ Linear, no branching.
▸ Found in tubers and roots of dahlias, onions, garlic
▸ Hydrolysis yields fructose
▸ Soluble in water but not hydrolyzed by intestinal enzymes and has
no nutritional value
▸ Used to determine the GFR
▸ for rehydration following loss of water
▸ vaccine adjuvant
14

15. Cellulose (Structural)
▸ Fibrous, tough, water insoluble substance found in the cell walls of plants,
particularly in stalks, stems, trunks, and all the woody portions of the plant
▸ Mass of wood and cotton is almost pure cellulose
▸ a polysaccharide of glucose units in unbranched linear chains
▸ Has (β1→4) glycosidic bonds.
▸ Cannot be digested by humans because humans cannot break down (β1→4)
glycosidic bonds.
▸ However, termites, wood fungi and some ruminants can use it as a source
of energy
15

16. 16

17. Chitin
▸ Principal component of the exoskeleton of arthropods.
▸ Consists of N-acetyl glucosamine residues with a beta-1,4-linkage.
▸ Only difference from cellulose is the replacement of the hydroxyl group at C-
2 with an acetylated amino group.
▸ Second most abundant in nature.
▸ Chitin is used commercially in coatings(extends the shelf life of fruits and
meats)
17

18. 18

19. Heteropolysaccharides
▸ Heteropolysaccharides are the polysaccharides composed of
different types of sugar and their derivatives
▸ Mucopolysaccharides or Glycosaminoglycans are carbohydrates
containing a repeating disaccharide namely amino sugars and
uronic acids.
19

20. Agar
▸ a mixture of sulfated heteropolysaccharide made up of D-galactose
and L-galactose derivative either-linked between C-3 and C-6..
▸ Used as supporting agent to culture bacterial colonies and
production of capsules
20

21. Agarose:
▸ the agar component with charged groups (sulfates, pyruvates) gel-
forming property so Agarose gels are also used for the
electrophoretic separation
21

22. Glycosaminoglycans (Mucopolysaccharides)
▸ complex carbohydrates of extracellular matrix, unbranched
polysaccharide made up of repeating disaccharides units so each
contains
A) Amino sugar – is either glucosamine or galactosamine.
B) Acid sugar – is Glucoronic acid or in some there is irudonic acid
▸ Hold large quantities of water and occupy space
▸ form a meshwork with fibrous proteins like collagen, elastin,
fibronectin etc which is known as Extracellular matrix.
22

23. Hyaluronic acid (hyalos- glass)
▸ Around 50, 000 repeats of the basic disaccharide unit
▸ contains alternating residues of D-glucuronic acid and N-
acetylglucosamine linked by (β1→4) and (β1→3) linkages
▸ Present in basement of glomerulus of kidney, connective tissues,
cartilage, synovial fluid and vitreous humor
23

24. Chondroitin sulfate (Chondros- catilage)
• Widely distributed in cartilage, tendons, ligaments, and the wall of
the aorta and also helps in compressibility of cartilage
• Around 20-60 repeated units of D-glucoronic acid and N-acetyl D-
galactosamine-4 sulphate linked by (β1→3) and (β1→4) linkage.
24

25. Dermatan sulfate (Derma- skin)
▸ Structurally related to Chondroitin Sulphate
▸ Found in skin, blood vessels and heart valve, sclera
▸ Repeated units of L-iduronic acid and N-acetylgalactosamine in (α
1→3) linkages
25

26. Keratan Sulphate:(Keras- horn)
▸ Does not contain uronic acid, sulfate content varies
▸ Formed by alternating units of D-Galactose and N-Acetyl-
Glucosamine-6-sulphate in beta 1-4 linkage
▸ Found in cornea maintains transparency(I), and found in variety of
horny structures formed of dead cells(II)
26

27. Heparan sulphate: (hepar-liver)
▸ Formed by repeated units of sulphated glucosamine and L-iduronic acid by α
1→4 linkage
▸ Heparin is a fractionated form of heparan sulfate derived mostly from mast
cells
▸ used as anticoagulant as it binds antithrombin (activates antithrombin)
27

28. GLYCOCONJUGATES
Carbohydrates covalently joined to protein or lipid.
Information carriers
 Three types:
 Proteoglycans
 Glycoproteins
 Glycolipids
28

29. Proteoglycans
▸ Proteoglycans are conjugate proteins and it is estimated that
mammalian cells can produce 40 types of proteoglycans.
▸ Proteins called “core” proteins are covalently linked to
glycosaminoglycans.
▸ Amount of carbohydrates in proteoglycans are 95% more as
compared to glycoproteins
29

30. Core proteins are covalently linked to glucosaminoglycans attached via
tetrasaccharide bridge at the serine residue.
The Ser residue is generally in sequence –Ser – Gly –X – Gly (where X is any
amino acid residue)
30

31. Many proteoglycans are shed into ECM also.
Example includes basal lamina, the sheet like ECM, contains a core proteins,
each with several covalently attached heparan sulfate chains.
There are 2 major families of membrane heparan sulfate proteoglycans
• Syndecans: have single transmembrane domain and an extracellular domain
• Glypicans: are attached to membrane by a lipid anchor
Both of these can be shed into extracellular space in the form of syndecan
ectodomains and glypicans
31

32. 32

33. ▸ Proteoglycan aggregate:
• Is the enormous aggregate of many core proteins all bound to single
molecule of hyaluronan which is found in ECM
• Aggrecan core protein has multiple chains of chondroitin and
keratan sulfate joined to serine residue through trisaccharide linkers
• Interact strongly with collagen in ECM of cartilage contributing to
development, tensile strength and resiliency of the tissue
33

34. 34

35. Functions of Proteoglycan
▸ It acts as constituent of ECM or ground substances.
▸ Plays a vital role in release of hormones.
▸ It maintain shape of sclera and also plays a role in corneal
transparency.
▸ Acts as anticoagulant
▸ It plays a role in compressibility of cartilage, collagen provides
tensile strength and aggrecan act as shock absorber.
35

36. Glycoproteins
▸ Severe proteins covalently bound to carbohydrates which are
referred to as glycoproteins.
▸ Carbohydrates play a major role in protein – protein recognition
▸ Almost all the plasma proteins of humans .
▸ Many proteins embedded in cell membranes, in making number of
blood group substances (A B O AB) even (+/-)
36

37. ▸ Two different types of oligosachharide linkage in glycoproteins.
37

38. 38

39. Glycolipids and Lipopolysaccharides
▸ Some lipids too have covalently bound oligosachharides.
▸ Gangliosides
▹ Are eukaryotic membrane lipid and in vertebrates ganglioside
carbohydrate composition helps In determining blood groups.
▸ Lipopolysaccharides
▹ Structure in the outer surface of gram(-) bacteria (Escherichia
coli, Salmonella typhimrium)
▹ Prime immunological target of antibodies produced by immune
system in response to infection
▹ Some are toxic to animals
39

40. Fig. Bacterial
lipopolysaccharide

41. Carbohydrate as informational molecules: The sugar
code
▸ There are specific carbohydrate binding proteins that read the sugar
code and mediate many biological processes
▸ They 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
▸ Lectins promote interactions between cells
41

42. Are organized into different classes on basis of their amino acid sequences and
biochemical properties
▸ C lectins: The C-type designation is from their requirement for calcium for
binding in animals, these proteins have amino acids that is responsible for
carbohydrate binding
▸ L lectins:- specially rich in seeds of leguminous plants, calnexin & calreticulin
are prominent chaperones in eukaryotic ER.
▸ Selectins bind specifically to carbohydrates on lymph node vessels,
endothelium or activated platelets respectively
▸ L selectin also produced by embryos when they are ready to attach to
endometrium of the mother’s uterus.
42

43. ▸ Selectins (plasma membrane lectins)
43

44. Lectins in development of diseases
Hemagglutinin (Lectin of Influenza virus)
Essential for viral entry and infection.
Interaction with sialic acid residue  entry & newly synthesized bud-out
Sialidase (Neuraminidase)
Cleavage of sialic acid  Viral particles.
Target for antiviral drugs: Oseltamivir, Zanamivir.
44

45. Bacterial Adhesion by Lectins
 Helicobacter pylori
 Responsible for gastric ulcers.
 Bacterial membrane lectins.
 Interaction with oligosaccharide Lewis b of
gastric epithelial cells which is part of
type O blood group determinant.
45

46.  Vibrio cholerae (cholera toxin)
 Attach to oligosaccharide of ganglioside GM1 on the surface of
host epithelial cell.
 Bordetella pertussis
 Enters target cells after interacting with host oligosaccharide
with a terminal sialic acid.
46

47. REFERENCES
Lehninger Principles of Biochemistry 6th edition
Harper's Illustrated Biochemistry 31st edition
Textbook of Medical Biochemistry – Dinesh puri
U. Satyanarayana Biochemistry 4th edition
https://www.ncbi.nlm.nih.gov
47

48. “ There's always going to be
growth, improvement, adversity;
you just got to take it all in and do
what's right, continue to grow,
continue to live in the moment.

49. 49
THANK YOU