Polysaccharides are long carbohydrate molecules composed of repeated monosaccharide units joined by glycosidic bonds. They can be classified as homopolysaccharides containing a single monosaccharide or heteropolysaccharides containing multiple monosaccharides. Polysaccharides serve important structural and storage functions in organisms. Their solubility is determined by factors like branching, molecular weight, charged groups, and regularity of structure. Capsular polysaccharides allow bacterial classification and are targets for vaccine development against pathogens like Salmonella Typhi, Haemophilus influenzae, and Neisseria meningitidis.

1. POLYSACCHARIDES
structures and properties
Mohammad Mainudduin
Incepta vaccine Ltd
Research & Development
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2. TOPICS
• Definitions & Classifications
• Functions of Polysaccharides
• Structure of LPS
• Structure of capsular polysaccharides
• Salmonella Typhi (Vi)
• Haemophilus influenzae
• Pneumococcal polysaccharides
• Meningococcal polysaccharides
• Main moieties of PS
• Polysaccharides and Solubility
• Structure and Solubility
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3. Definitions & Classifications
POLYSACCHARIDES-
Polysaccharides are long carbohydrate molecules of repeated monomer units joined
together by glycosidic bonds. A polysaccharide may contain anywhere from a few
monosaccharides to several thousand monosaccharides.
Its also called Complex carbohydrates.
Polysaccharides have a general formula of Cx(H O)y , where x is usually a large number
between 200 and 2500.
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4. Definitions & Classifications.
Another term for the polysaccharides is the “Glycans“. According to Whistler’s
classification, polysaccharides can be divided into two types.
They are
HomoGlycans: These are made up of a single monosaccharides. Eg: Starch, Cellulose,
Glycogen, and Inulin
HeteroGlycans: These are composed of two or more kinds of monosaccharides (or their
derivatives), such as mucopolysaccharides, be called “heteroglycans”.
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5. Definitions & Classifications..
1. The polysaccharides made with Glucose is called “Glucans”
2. The polysaccharides made with Fructose is called “Fructans”
3. The polysaccharides made with Mannose is called “Mannans”
4. The polysaccharides made with Xylose is called “Xylans”
I. HOMOPOLYSACCHARIDES-
 A.Cellulose-
Cellulose is the main structural material of trees and other plants. The general formula of Cellulose is (C6H10O5)n. Wood is
50% cellulose, while cotton wool is almost pure cellulose.
Structure- Cellulose is a linear polymer of D-glucose residues bonded by β(1, 4)-O-glycosidic linkages. It is the most
abundant carbohydrate in nature.
Properties:
Cellulose is a colorless amorphous solid having no melting point. It decomposes on strong heating. it is insoluble in water
and most organic solvents. However, it dissolves in Schweitzer’s reagent which is an ammoniacal solution of cupric
hydroxide.
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6. Definitions & Classifications…
B. Starch
Starch is the second most abundant carbohydrate in nature. It is the main contributor of carbohydrates in our diet. It exists
only in plants, stored in the seeds, roots, and fibers as a food reserve. The chief sources of starch are cereals, potatoes, corn,
and rice.
Structure:
Starch is actually a mixture of two structurally different polysaccharides – Amylose (20%) and Amylopectin (80%). When
starch is heated with hot water, it can be separated into these components. The part soluble in water is amylose and the
remaining fraction is amylopectin.
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7. Definitions & Classifications….
There are are two types of glycosidic bonds - 1,4 alpha and 1,4 beta glycosidic bonds. 1,4 alpha glycosidic bonds are formed when
the OH on the carbon-1 is below the glucose ring; while 1,4 beta glycosidic bonds are formed when the OH is above the plane.
II. HETERO POLYSACCHARIDES
Heteropolysaccharides contain two or more different monosaccharides. Usually, they provide extracellular support
for organisms of all kingdoms: the bacterial cell envelope, or the matrix that holds individual cells together in animal
tissues, and provides protection, shape, and support to cells, tissues, and organs.
Hyaluronic acid, chondroitin sulfates, and dermatan sulfates are important heteropolysaccharides in the
extracellular matrix. These heteropolysaccharides usually are formed by the repetition of a disaccharide unit of an
aminosugar and an acid sugar.
A. Hyaluronic Acid (Hyaluronate)
B. Chondroitin Sulfates
C. Dermatan Sulfate
D. Keratan Sulfate
E. Heparin
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8. Functions of Polysaccharides
Polysaccharides form a crucial part of cell function and
structure.
Storage polysaccharides: Polysaccharides such as starch and
glycogen are called storage polysaccharides because they are
stored in the liver and muscles to be converted to energy later
for body functions. Starch is found in plants whereas glycogen is
found in animals.
Structural polysaccharides:
Cellulose- found in the cell walls of plants.
Another structural polysaccharide is chitin.
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9. Structure of LPS
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10. Structure of capsular polysaccharides
• High molecular weight (50,000 to >106 Da)
• Repeat units consisting of up to 10 sugars
• Most capsular polysaccharides are negatively charged
• Uronic acids
• Sialic acids
• Phosphate groups
• Some are neutral (pneumo 7F, 14, 22F and 33F)
• Some are zwitterionic (+ and – charges)
• Large range of monomeric units (at least 100 known)
• Structure is linear or branched
• Wide variety of linkage positions
• No real secondary or tertiary structure
• Only stable repeat unit is a helix
• Helix is ill-defined and flexible
• Epitopes are essentially primary and not dependent on complex folding as in proteins
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11. Salmonella Typhi (Vi)
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O
NH
O
O COO-
O
C
H3C
N-acetyl-a-D-galactosaminuronic acid
2,000 to 10,000 repeating units

12. Haemophilus influenzae
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poly ribosyl-ribitol phosphate PRP
H. influenzae is differentiated based on its type
capsule.
H. influenzae serotype b was a leading cause of
disease in infants and children There are six
distinct serological types (a–f) of encapsulated
H. influenzae.
95% of all serious infections are attributed to
type b

13. Pneumococcal polysaccharides
• Pneumo CPS have repeat units of 2-8 sugars
• Most are anionic
• Some unusual sugars (e.g. pneumosamine)
• O-acetylation is frequent
• Some have carboxyl groups
• Generally of large molecular weight
• At least 90 serogroups, lower number associated with disease
• Current polysaccharide vaccine contains 23 serotypes (25 µg each)
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Prevnar 13

14. Meningococcal polysaccharides
• Meningococcal meningitis caused by 5 of 12 serogroups of Neisseria meningitidis
• Most disease occurs in the young and Group B is the prominent cause.
• Group B polysaccharide is not suitable for vaccine use
• A secondary peak of disease occurs in teenagers especially in group situations (group C common in this
peak)
• Group A is the cause of epidemic meningitis in sub-Saharan Africa and in India
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15. Main moieties of PS
• O-Acetyl-
• N-Acetyl-
• Sialic acid
• PRP
• Vi
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16. Polysaccharides and Solubility
Polysaccharides have very complex structural features. i.e-
-Monosaccharide composition
-Glycosidic bonds (linkage patterns)
-Degree of branching
-Molecular weight distribution
-And the presence of special groups.
These structural features highly affected the solubility of polysaccharides, in either
positive or negative way.
Any structure that hinders the intermolecular association usually leads to a higher
solubility,
-such as branching structure
-charged group (carboxylate group
-sulfate, or phosphate groups)
On the opposite, structural characters that promote the intermolecular association result in the poor
solubility
-such as linear chain
-large molecular weight
-and other regular structural characters.
NB:-It should be noted that these structural features are not isolated but inter correlated with each
other to decide the solubility of any specific polysaccharide.
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17. Polysaccharides and Solubility…
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18. Polysaccharides and Solubility…
• Neutral Polysaccharides Generally the extra cellular polysaccharides are composed of monosaccharides
with hexoses (glucose, galactose, mannose, xylose, rhamnose and arabinose) and/or pentoses forming the
bulk of it. The monosaccharides are significant factors in determining both the surface charge and settling
properties. They also determine rheological properties of suspensions.
• Acidic polysaccharides In acidic extra cellular polysaccharides the uronic acid is one of the monomeric unit.
It strongly influences the physical properties due to the presence of charged anionic groups on these
polysaccharides that can strongly interact with the cations.
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19. Structure and Solubility
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