Download Glycosaminoglycans and Glycoprotein

Glycosaminoglycans and Glycoprotein
Objectives
- Recognize the different classes of glycosaminoglycan and
their functions.
- Know what are the proteoglycans, function and the general
structure.
- Glycoproteins and blood-group substances as example
*Glycosaminoglycan
-Structure
-classification
-Functions
*Glycoproteins
-structure and functions
-O- and N-linked oligosaccharides
-Blood group substances
Glycosaminoglycans
Glycosamines: sugar derivatives in which the hydroxyl group at C2 is replaced
with NH2 group.
Structure of Glycosaminoglycans
Glycosaminoglycans (GAGs): large complexes of negatively charged linear
heteropolysaccharides chains. These polymers consist of repeating
disaccharide unit (acidic sugar-amino sugar).
The amino sugar is either Nacetylglucosamine or Nacetylgalactosamine. The
acidic sugar is–uronic acid
usually D-glucouronic acid,
some hydroxyl groups are
esterified with sulfate.
These compound have special
ability to bind large amounts
of water, so produce gel-like
matrix
Functions of Glycosaminoglycans
∗ GAGs are component of the extracellular matrix; a gel-like
material that fill the extracellular space in the tissues of multicellular animals. GAGs form an interlocking meshwork with the
fibrous protein as fibronectin, collagen, elastin
∗ Responsible of the viscous, lubricant properties of mucous
secretions and for this GAGs were called mucopolysaccharides
∗Stabilize and support cellular and fibrous component of the
tissue; connective tissue (found in skin, tendons, cartilages….) they
are consist of insoluble protein fibers distributed in the ground
substance
The character of the connective tissue is dependent on the
relative proportions of the ground substance and embedded
fibrous protein
Classification of
the
Glycosaminoglycans
They can be classified
according to to their
monomeric
compositions, type of
glycosidic linkages,
and degree of their
sulfate units.
Glycoconjugates: Proteoglycans,Glycoproteins, and Glycolipids
Polysaccharides are not only stored fuels and structural elements but also
considered as information carriers
- serve as destination markers for some protein
-cell-cell recognition and adhesion, cell migration, blood clotting and immune
response
*The informational carbohydrates are usually covalently joined to a protein or
lipid to form Glycoconjugate
Glycoprteins: have one or several oligosaccharides of varying complexity joined
covalently to proteins.
They present at the outer side of the plasma membrane, extracellular matrix, and
blood.
Highly specific sites for recognition and high-affinity binding by other protein.
Glycolipids: are membrane lipids, the hydrophilic head groups are oligsaccharides
and act as specific sites for recognition by carbohydrate-binding proteins.
Proteoglycans: macromolecules of cell surfaces or extracellular matrix in which
glycosaminoglycan chains are joined covalently to a membrane protein. The
glycosaminoglycan moiety forms the greater fraction of proteoglycanmolecule
Glycoproteins
Glycoproteins: are proteins to which oligosaccharides are covalently
attached, the length of carbohydrate moiety is: relatively short compared
to glycosaminoglycans, branched and may or may not negatively charged.
Glycoproteins contain highly variable amounts of carbohydrates ,
IgG contains less than 4%
Glycophorin (in the red blood cells) contains more than 20%
Mucin (human gastric glycoprotein) contains more than 60%
Advantages of adding oligosaccharides to proteins
- Affects the polarity and solubility
- affects the folding pathway of the proteinÎ affects the tertiary
structure
- each oligosaccharide represents a unique face that can be recognized by
enzyme, signal and receptor which can interact with it
Glycoproteins
Functions:
*membrane bound glycoproteins
participate in many cellular phenomena
including
-cell surface recognition by other cells,
hormones, viruses
-cell surface antigenicity as blood group
antigen
*components of extracellular matrix, and
of the mucins of the gastrointestinal tract
and they act as protective biological
lubricants.
Structure of Glycoproteins
The carbohydrate moiety is attached at its anomeric carbon through glycosidic
link to the –OH of the serine or Threonine ( O-glycosidic link) or to the amide
group of the Asparagine side chain(N-glycosidic link)
A glycoprotein may contain N- and/ or O-linked glycosidic linkage
O-linked oligosaccharides are found as membrane glycoprotein components or
extracellular glycoproteins, e.g glycoprotein that provide ABO blood grouping
N-linked oligosaccharides fall into two classes: complex oligosaccharides and high
mannose oligosaccharides
Structure N-linked oligosaccharides
The carbohydrate moiety is attached at
its anomeric carbon through glycosidic link
to the amide group of the Asparagine side
chain
N-linked oligosaccharides fall into two classes:
complex oligosaccharides and high mannose
oligosaccharides
Blood Group substances
Blood group antigens are an important group of polysaccharide that
attached as O-linked glycans to membrane proteins in some cell, or can be
linked to a lipid molecule to form a glycolipid. These oligosaccharides that
determine the blood group types (ABO)
*all humans can produce can produce type O-oligosaccharides
Addition of N-acetlygalactosamine by
glycosyltransferase produces type A antigenÎ
blood type A
Addition of Galactose by the enzyme galactosyltransferase
makes type B antigen Î blood type B
* Humans possess no enzymes Î blood Type O
* With the two enzymes Î blood type AB, both A and B
oligosaccharides are present on the cell surface
Transfusion relation ships between blood types
Humans can produce antibody against A, B antigen, but type Opolysaccharides are non antigenic.
•No one produce antibody against his own antigen but produces them
against the other antigen.
•Transfusion relation ships between blood types
-type O is universal donor
-type AB universal acceptor
The End