INTRODUCTION STRUCTURE TYPES OF BONDS N-LINKED GLYCOSYLATION O-LINKED GLYCOSYLATION AMOUNT OF CARBOHYDRATES PRESENT IN GLYCOPROTEIN BIOLOGICAL SIGNIFICANCE AND FUNCTION BIOLOGICAL ADVANTAGE OF ADDING OLIGOSACCHARIDES TO PROTEIN

1. Glyco- & lipo- proteins
1
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )

2. SYNOPSIS for Glycoproteins
 INTRODUCTION
 STRUCTURE
 TYPES OF BONDS
 N-LINKED GLYCOSYLATION
 O-LINKED GLYCOSYLATION
 AMOUNT OF CARBOHYDRATES PRESENT IN GLYCOPROTEIN
 BIOLOGICAL SIGNIFICANCE AND
 FUNCTION
 BIOLOGICAL ADVANTAGE OF ADDING OLIGOSACCHARIDES TO
PROTEIN

3. INTRODUCTION
Glycoprotein have been defined as conjugated proteins
which contains one or more saccharides lacking a serial repeat
unit and are bound covalently to a protein.
Glycoproteins are resultant from the covalent attachment
of carbohydrate chains both linear and branched in structure to
various sites on the polypeptide backbone of a protein.
Glycoproteins are conjugated proteins which are
biologically active molecules. In Glycoprotein the prosthetic part
is carbohydrate.

4. Fig:- structure of glycoprotein present in
plasma membrane

5. STRUCTURE
 Covalent linkage of a sugar to the proteins is a central part
of Glycoprotein structure.
 Among the several different classes of conjugated proteins
Glycoprotein's are one of them which represent a large
group of conjugated proteins with their biological
significance.
 Carbohydrates are linked to proteins by N or O – linkage or
N – or O – glycosyl bonds.
1. N - Glycosyl linkage to asparagine.
2. O – Glycosyl linkage to serine.

6.  N-linked glycosylation is important for the folding of some eukaryotic
proteins.
•The N-linked glycosylation process occurs in eukaryotes and widely in
archaea, but very rarely in bacteria.
• For N-linked oligosaccharides, a 14-sugar precursor is first added to
the asparagines in the polypeptide chain of the target protein.
•The structure of this precursor is common to most eukaryotes, and
contains 3 glucose, 9 mannose, and 2 N-acetylglucosamine
molecules.
N-linked Glycosylation

7. Structure of N-linked glycosylation

8.  O-linked glycosylation occurs at a later stage during protein
processing, probably in the Golgi apparatus.
• This is the addition of N-acetyl-galactosamine to serine or threonine
residues by the enzyme UDP-N-acetyl-D- galactosamine:polypeptide N-
acetyl galactosaminyl transferase followed by other carbohydrates (such
as galactose and sialic acid).
• This process is important for certain types of proteins such as
proteoglycans, which involves the addition of glycosaminoglycan chains
to an initially unglycosylated "proteoglycan core protein."
O-linked Glycosylation

9. Structure of O-linked glycosylation

10. STRUCTURE OF LINKAGE

11. Amount of carbohydrates in glycoprotein
Glycoprotein Amount of
carbohydrate
1. IgG
2. Glycophorin
3. Human ovarian cyst
4. Human gastric
glycoprotein
5. FSH
6. LH
7. TSH
8. Chorionic gonadotropin
4%
60%
70%
82%
18.2%
15.7%
16.2%
31%

12. BIOLOGICAL SIGNIFICANCE
 Glycoproteins in cell membranes may have an important role in
the behavior of cell and especially in the biological function of the
membrane.
 Glycoproteins are constituents of the mucus secreted by certain
epithelial cells, where they mediate lubrication and protection of
tissues lining the respiratory, gastrointestinal and female
reproductive system.
 Many secreted protiens are glycoproteins and they also includes
a) Hormones :- FSH, LH, TSH, chorionic gonadotropin.
b) Plasma proteins:- Orosomucoids, ceruloplasmin, plasminogen,
prothrombin and immunoglobulins.

13. FUNCTION
• The role of carbohydrates in glycoprotein structure/function
seems to involve their role in directing proper folding of proteins
in the ER .
•In cell membrane they help to stabilise the membrane structure
as they forms hydrogen bonds with water molecules in the fluid
surrounding the cell.
•The most important function of glycoprotein in animal cell is to
increase the strength and impermeability of the outer bilipid
layer.
•Defence against infection:- IgG, interferon.

14.  The biological advantages of adding oligosaccharides to protein are not
fully understood. The very hydrophilic clusters of carbohydrates alter the
polarity and solubility of the proteins with which they are conjugated.
 Steric interaction between peptide and oligosaccharides may preclude one
folding route and favor another.
 The bulkiness and negative charge of oligosaccharides chains also protect
some proteins from attack by proteolytic enzymes.
 Many glycoprotein helps in lubrication and protection such as EPITHELIAL
MUCINS, SYNOVIAL FLUID etc.
 LECTINS are protein which are helpful to determine and separating
glycoprotein with different oligosaccharides and serve in cell-cell
recognition,signaling & adhesion process and intra cellular targetting of newly
synthesized protein.
BIOLOGICAL ADVANTAGES OF ADDING
OLIGOSACCHARIDES TO PROTEIN

15. Synopsis for Lipoproteins
 INTRODUCTION
 TYPES OF LIPOPROTEINS
 COMPOSITION OF LIPOOPROTEIN
 TRANSPORT OF LIPOPROTEIN INSIDE THE CELL
 TRANSPORT OF LIPOPROTEIN IN HUMAN BODY
 BIOLOGICAL ADVANTAGE OF ADDING LIPIDS TO PROTEIN
/ FUNCTIONS OF LIPOPROTEINS
 CONCLUSION
 REFERENCES

16. 16
 What are lipoproteins and why do we need them?
 Lipoproteins are a handful of different molecules
that interact with water insoluble fat molecules, and
transports those fats in the plasma.
 Different lipoproteins are responsible for the
transportation of different fats.
 Lipoproteins allow fat to be dissolved into the
plasma.
 Function: Transport of fat soluble substances

17. 17
 There are 4 types of lipoproteins
 Chylomicrons
 Transport of dietary triglycerides from the GI tract to
the liver
 Very Low Density Lipoproteins ( VLDL )
 Transport of triglycerides from the liver to tissues for
storage and energy
 Low Density Lipoproteins ( LDL )
 Transports cholesterol to peripheral tissues
 High Density Lipoproteins ( HDL )
 Transports cholesterol away from the peripheral
tissues to the liver

18. 18
 Lipid Chemistry
 Lipids include
 Cholesterol
 Triglycerides
 Phospholipids
 Glycolipids
 Lipids are important components of cell membranes

19. 19
 Fatty acids are short to long carbon chained
molecules
 Saturated fatty acids
 No double bonds between carbons ( C – C )
 Solid at room temperature
 Animal sources
 Unsaturated fatty acids
 Double bonds between carbon bonds ( C = C)
 Usually liquid at room temp
 Plant sources

20. 20
 Triglycerides
 Glycerol with 3 attached fatty acids.
 95 % of body fat is triglycerides.
 Energy source when plasma glucose is decreased.
 Triglyceride catabolism is regulated by lipase,
epinephrine and cortisol.
 Triglycerides transported by Chylomicrons
(exogeneous) and VLDL (endogenous).

21. 21
 Cholesterol
 Found only in animals.
 Important component of membranes, steroid
hormones, bile and Vitamin D.
 Exogeneous cholesterol comes from diet.
 Endogeneous cholesterol is synthesized by the liver.
 70 % of cholesterol associated with cellular
components.
 30 % is in the plasma ( ⅓ free form , ⅔ esterfied )
 Transported by HDL and LDL

22. 22
 Apolipoproteins
 Outer protein “shell” of the lipoprotein molecule.
 The protein – lipid interaction allows the water
insoluble lipid to become soluble in plasma.
 The apolipoprotein is responsible for the
interactions with cell membranes and enzymes to
transport lipids to specific locations.

23. 23
 Lipoproteins
 Classified according to density and electrophoresis
migration.
 Lipoproteins differ in their sizes, weights, chemical
composition, etc.
 There are four main types of lipoproteins
 CHYLOMICRONS
 VLDL
 LDL
 HDL

24. 24
 Chylomicrons
 Transports exogeneous ( dietary ) triglycerides.
 90 - 95 % by weight is triglycerides.
 Absent from fasting plasma.
 Inadequate clearance produces a creamy layer on the
plasma.
 VLDL ( Very Low Density Lipoproteins )
 Transports endogeneous triglycerides from liver to tissues.
 50 - 65 % by weight is triglycerides.
 Excess dietary carbohydrates are converted to triglycerides
by the liver.
 Once VLDL looses much of its TG’s it becomes LDL

25. 25
 LDL ( Low Density Lipoproteins )
 Transports cholesterol from liver to the tissues.
 Synthesized in the liver.
 Approximately 50 % by weight cholesterol.
 Most atherogenic lipoprotein … “ Bad Cholesterol“.
 HDL ( High Density Lipoprotein )
 Transports excess cholesterol from the tissues back
to the liver ( reverse transport ).
 Synthesized in the liver and intestines.
 Composition:
 30% PHOSPHOLIPIDS
 20% CHOLESTEROL
 50% APOPROTEIN
 The “good “ cholesterol.

26. Lipoprotein
class
Density
(g/mL)
Diameter
(nm)
Protein %
of dry wt
Phosphol
ipid %
Triacylglycerol
% of dry wt
HDL 1.063-1.21 5 – 15 33 29 8
LDL 1.019 –
1.063
18 – 28 25 21 4
IDL 1.006-1.019 25 - 50 18 22 31
VLDL 0.95 – 1.006 30 - 80 10 18 50
chylomicrons < 0.95 100 - 500 1 - 2 7 84
Composition and properties of human
lipoproteins

27. Lipoprotein structure

28. As VLDL particles are transported in the bloodstream, Lipoprotein
Lipase catalyzes triacylglycerol removal by hydrolysis.
With removal of triacylglycerols and some proteins, the % weight that is
cholesteryl esters increases.
VLDL are converted to IDL, and eventually to LDL.
VLDL  IDL  LDL
The lipid core of LDL is predominantly cholesteryl esters. Whereas
VLDL contains 5 apoprotein types (B-100, C-I, C-II, C-III, & E), only one
protein, apoprotein B-100, is associated with the surface monolayer of
LDL.
Tranport of Lipoproteins to Cells -

29. •After the clathrin coat
disassembles, the vesicle fuses
with an endosome.
•LDL is released from the
receptor within the acidic
environment of the endosome,
and the receptor is returned to
the plasma membrane.
•After LDL is transferred to a
lysosome, cholesterol is
released & may be used, e.g., for
• Cells take up LDL by receptor-
mediated endocytosis, involving
formation of a clathrin-coated pit
& pinching off of a vesicle
incorporating the receptor & LDL
cargo.
LDL
extracellular space
LDL
receptor
receptor-mediated
endocytosis
cytosol
Receptor Mediated Endocytosis -

32. CONCLUSION
Glycoprotein are important glycoconjugates. They are covalently attach
to carbohydrates. They are found on the outer face of the plasma
membrane, in the extra cellular matrix and in the blood.
Inside cells they are found in specific organelles such as golgi complex,
secretory granules and lysosomes where they perform various function.
Glycoprotein has various biological advantages and their study is very
important in AIDS,INFLUENZA and other diseases.
Lipoproteins are also important lipoconjugates, which are helpful in the
transportation of Lipid molecules in the inside the human body.

33. REFERENCE
1. TEXT BOOK OF BIOCHEMISTRY
LEHNINGER NELSON & COX (iv EDITION)
2. TEXT BOOK OF BIOCHEMISTRY
WILSON & WALKER