Glycoprotein, lipoprotein, structure and function

INTRODUCTION
DEFINITION
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 structure & function
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
• DEFINITION
• 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 boundcovalentlyto a protein.
Glycoproteins are resultant from the covalent attachment
of carbohydrate chains both linear and branchedin structure to
various sites on the polypeptide backbone of a protein.
Glycoproteins are conjugated proteins which are
biologically activemolecules. In Glycoprotein the prosthetic part
is carbohydrate.

4. DEFINITION OF GLYCOPROTEIN
Glycoprotein's are proteins with covalent or non covalent
attachment of carbohydrates with variable carbohydrate content.

5. STRUCTURE
•Covalent linkage of a sugar to the proteinsis 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.

7. N-linked glycosylation is important for the folding of some
eukaryotic proteins.
•The N-linked glycosylation process occurs in eukaryotesand
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 precursoris common to most eukaryotes,
and contains 3 glucose, 9 mannose, and 2 N-acetylglucosamine
molecules.
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. 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%

11. BIOLOGICAL SIGNIFICANCE
•Glycoproteins in cell membranesmay 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 andprotection of tissueslining 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.

12. FUTNCION
•Theroleofcarbohydratesinglycoproteinstructure/function
seemstoinvolvetheirroleindirectingproperfoldingofproteins
intheER.
•Incellmembranetheyhelptostabilisethemembranestructure
astheyformshydrogenbondswithwatermoleculesinthefluid
surroundingthecell.
•Themostimportantfunctionofglycoproteininanimalcellisto
increasethestrengthandimpermeabilityoftheouterbilipid
layer.
•Defenceagainstinfection:-IgG,interferon.

13. Synopsis for Lipoproteins
•INTRODUCTION
•DEFINITION
•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

14. •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
14

15. DEFINITION OF LIPOPROTEIN
Lipoproteinsare molecules made up of proteins and fat.

16. •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
16

17. •Lipid Chemistry
–Lipids include
•Cholesterol
•Triglycerides
•Phospholipids
•Glycolipids
–Lipids are important components of cell membranes
17

18. –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
18

19. •Triglycerides
–Glycerol with 3 attached fatty acids.
–95 % of body fat is triglycerides.
–Energy source when plasma glucose is decreased.
–Triglycerides transported by Chylomicrons(exogeneous) and VLDL
(endogenous).
19

20. •Cholesterol
–Found only in animals.
–Important component of membranes, steroid hormones, bile and
Vitamin D.
–Exogeneouscholesterol comes from diet.
–Endogeneouscholesterol 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
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21. •Apolipoproteins
–Outer protein “shell” of the lipoprotein molecule.
–The protein –lipid interaction allows the water insoluble lipid to
become soluble in plasma.
–The apolipoproteinis responsible for the interactions with cell
membranes and enzymes to transport lipids to specific locations.
21

22. •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
22

23. •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 endogenous 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
23

24. •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.
24

25. Lipoprotein
class
Density
(g/mL)
Diameter
(nm)
Protein %
of dry wt
Phosphol
ipid %
Triacylglycerol
% of dry wt
HDL 1.063-1.215 –15 33 29 8
LDL 1.019 –
1.063
18 –28 25 21 4
IDL 1.006-1.01925 -50 18 22 31
VLDL 0.95 –1.00630 -80 10 18 50
chylomicrons< 0.95 100 -500 1 -2 7 84
Composition and properties of human
lipoproteins

26. Lipoprotein structure

27. •Aftertheclathrincoat
disassembles,thevesiclefuses
withanendosome.
•LDLisreleasedfromthe
receptorwithintheacidic
environmentoftheendosome,
andthereceptorisreturnedto
theplasmamembrane.
•AfterLDListransferredtoa
lysosome,cholesterolis
released&maybeused,e.g.,for
membranessynthesis.
•CellstakeupLDLbyreceptor-
mediatedendocytosis,involving
formationofaclathrin-coatedpit
&pinchingoffofavesicle
incorporatingthereceptor&LDL
cargo.LDL
extracellular space

LDL
receptor
receptor-mediated
endocytosis
cytosol
Receptor Mediated Endocytosis-

29. •The lipoprotein allows fats to move through the water inside and outside cells
•Lipoprotein carry cholestrol & similar substance through the blood.
•The handling of lipoprotein particles in the body is reffered to as lipoprotein
particle metabolism.
FUNCTION

30. 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.
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 moleculesin the inside the human body.

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