N-linked Oligosaccharides and Glycosylation

Disaccharides

• Disaccharides are carbohydrates consisting of two monosaccharides linked together by a glycosidic linkage (GL).
• If the glycosidic linkage involves the carbonyl group (anomeric) of one sugar, the resulting disaccharide is non-reducing, e.g., sucrose
• If the glycosidic linkage involves the carbonyl group of one of its two sugars, the resulting disaccharide is reducing; e.g., lactose and maltose.
• Examples of disaccharides include maltose, lactose, and sucrose.
• Disaccharides consist of two covalently joined monosaccharides connected by an O-glycosidic bond, which is formed when a hydroxyl group of one sugar molecule reacts with the anomeric carbon of the other.

Reducing Disaccharides

• Classified into reducing and non-reducing disaccharides.
• Have a free anomeric carbon in the second sugar unit and exist in alpha and beta forms.
• Examples include maltose, isomaltose, and lactose.

Anomers

• Are cyclic monosaccharides that differ in configuration at C-1 (in aldoses) and C-2 (in ketoses).
• Cyclization induces two possible orientations of the hydroxyl group around the anomeric carbon atom (alpha and beta forms).
• The alpha-form has the OH group to the right of the anomeric carbon, and the beta-form has the OH group to the left of the anomeric carbon.
• The linkage between the aldehyde and alcohol or keto and alcohol groups is called 'hemiacetal' or 'hemiketal' linkage

Reducing Sugars

• Monosaccharides with a hemiacetal are reducing sugars because their open-chain form contains an aldehyde or alpha-hydroxy ketone.
• Their cyclic and open-chain forms exist in equilibrium.
• The "O" atoms tend to abstract electron from "H" atom and thereby, the “H” containing one electron, reacts with Metals by reducing them (i.e., they give away electrons)
• Are small carbohydrates, usually containing one or two sugar units, capable of acting as reducing agents towards certain metal salts. They are able to react with these salts because their cyclic hemiacetal functional group is able to equilibrate with an acyclic aldehyde.
• Metal salts have historically been used for testing purposes because they oxidize aldehydes and give a clear color change upon reduction.
• Acetals are "locked" and do not react.
• Any sugar containing a hemiacetal is a reducing sugar; the term "sugar" refers to mono- and di-saccharides, not complex carbohydrates like starch, glycogen, and cellulose.

Oligosaccharides

• Polymers consisting of 3-10 monosaccharide units.
• They are not a major source of carbohydrates in the human diet because most are non-digestible.
• Consistuent of ABO blood group substance, immunoglobulins, glycolipids, etc.

Polysaccharides

• Composed of more than 10 monosaccharide units linked by glycosidic bonds.
• Polysaccharides are non-reducing because carbonyl groups used in condensation, leaving only one free carbonyl group.
• Include homopolysaccharides and heteropolysaccharides.

Homopolysaccharides

• Polysaccharides entirely made of one type of monosaccharide unit.
• Named according to their building-unit nature.
• Glucans are formed of D-glucose units (starch, dextrin, glycogen, cellsuloses).
• Fructans are formed of D-fructose units (inulin present in plants).
• Starch is the chief storage form of carbohydrates in chlorophyll plants.
• Large amounts can be found in cereals, tubers and legumes.
• Starch granules contain two forms: amylose (15–20%) in the inner part and amylopectin (80–85%) in the outer part.
• Amylose is a molecule composed of approximately 300-400 alpha-D-glucopyranose molecules connected by alpha 1,4-glocosidic linkage.
• Amylopectin is a branches polysaccharide, composed of approximately 24-30 alpha-D-glucopyranose units linkes by alpha 1,4-glucosidic linkage within the branches and 1,6 linkage at branch points
• Dextrins are produced during starch hydrolysis from salivary/pancreatic amylase. Glycogen is the storage form of carbohydrates in animals, present mainly in skeletal muscles and liver.
• Glycogen has more frequent alpha-1,6-glucosidic branches in comparison to amylopectin.
• Cellulose forms the principal part of cell walls.
• Formed of a long non-branched chain of beta-D-glucopyranose units by Beta 1,4 linkages.
• Cellulose is insoluble in water meaning it does not give a colour with iodine.
• Cellulose can be hydrolyzed by strong acids or by cellulase (present in some bacteria).
• The presence of cellulose in the diet is important as it increases the bulk of food and prevents constipation.

Heteropolysaccharides

• Polysaccharides formed of more than one type of monosaccharide unit.
• Glycosaminoglycans (GAGs), also called mucopolysaccharides, are carbohydrate derivatives, but not polysaccharides or disaccharides.
• This is due to the Unbranched long chains usually contain over 50 sugar units made up of repeating disaccharide units, typically consisting of a uronic acid and an amino sugar
• GAGs may be divided into non sulfated GAGs and sulfated GAGs

Hyaluronic Acid

• Naturally an occurring biopolysaccharide.
• A polymer consisting of D-glucuronic acid and N-acetyl-D-glucosamine disaccharide units.
• Linked via alternating (beta 1,4) and (beta 1,3) glycosidic bonds.
• Hyaluronic acid has be 250000 disaccharide repeats in length
• Hyaluronic Acid is found in organisms from bacteria to animals, including humans
• Hyaluronic Acid is found in connective tissues, synovial fluids, the vitreous fluid, umbilical cords, chicken combs. Hyaluronic Acid is needed for wound repair
• Integral membrane proteins, known as hyaluronan synthases, synthesize Hyaluronic Acid. - Hyaluronic Acid is degraded by a family of enzymes known as hyaluronidases

Hyaluronic Acid Functions

• Maintenance of elastoviscosity of liquid connective tissues, e.g. synovial and eye vitreous fluid.
• Control of tissue hydration and water transport.
• Supramolecular assembly of proteoglycans in the extracellular matrix.
• Various receptor-mediated roles in cell detachment, mitosis,migration, tumor development, metastasis and inflammation.
• Due to binding water, Hyaluronic Acid lubricates parts like moveable joints/muscles.
• Hyaluronic Acid is an signalling molecule that takes parts in mammal biological, as well as roles in disease causing events.
• Bacteria make Hyaluronic Acid to encapsulate themselves and to escape being seen of the host system.

Glucosaminoglycans

• Further classified into sulfates that containing glucosaminoglycans (g. chondroitin sulphate, keratan sulphate, dermatan sulphate, heparin, etc.)

Chondroitin Sulfate

• Molecular weight is 5-50 kDa.
• It is most abundant GAG in the body.
• Found in ligament, aort, cartilage etc.
• Bind to proteins (like collagen) to create proteoglycan

Dermatan Sulfate

• Molecular weight is 15-40KDa.
• Found in vessels, skin and valves. Has L-Iduronic acid

Keratin Sulfate

• Molecular weight is 4-19kDa
• Most heterogeneous GAG.
• Found in cornea.
• Combined with aggregated cartilage

Heparin Sulfate

• Its glucosamine has less sulfate more so than heparin.
• Maintains communication from and between ECM/cells
• Stimulates adhesion of cells to ECM
• Binds to other matrix of macromolecules

Summary Of GAGs

• This table gives constituents and localizations, and highlights where they interact.
• Hyaluronic acid exists as synovial fluid and ground substance of connective tissue.
• Chondroitin sulfate can exists as cartilage and tendons, but is more prominent as GAG.
• Dermatoma sulfate exists as skin and heart valves
• Keratin Sulfate exists in Cornea

Proteoglycans

• Some GAGs have a protein core and become proteoglycans.
• Mostly carbs (95%), some proteins (5%).
• Theyre found mainly in ECM as ground.

GAG and proteoglycans' functions can be important matrix constituents that produce felixible ECM

• Serves to filter some membranes while slowing movement
• lubricant in some fluid
• can reduce ECM size from water squeeze or hydrate again

Glycoproteins

• Proteins to which oligosaccharide chains covalently bind
• Contents has less uronic acids/ repeating disaccharides
• Eight monosaccharides are present like galactose, glucose, mannose, xylose, fucose, N-acetylglucosamine, N, acetylgalactosamine and N-acetylneuraminic acid
• Carbohydrates exist in cel membranes, tissues.
• Glycoproteins is variable with collagen (1%), IgG (4%), Mucins (50%) and ABO antigens(85%)

AB Glycoproteins

• ABO blood depends of oligosaccharide parts

Glycoprotein links

• Glycoproteins are specified wwith location and streochemisty with alycosidic linkage

Glycoprotein Linkage

• glycosidic bond to the hydroxyl group of Ser or Thr residues
• oligosaccharides has a glycosidic linkage to amide nitrogen of Asn

Comparisons

• proteoglycans has repeating units where
• GlcNAc is n-acetyl
• Man is Mannose
• Neu5Ac is Neuraminic Acid
• GacNAac is Acetyl Gacatosamine
• Asn Asn residue or O-link
• In Glycoproteins glycosidic is specified and is where bonded is with strepchemistric bond

Glycoprotein differences

• in blood vs protein cell-cell where
• Chondrotin is dermatim
• they bind mostly at connexity vs. binding
  • Collagen transferrin mostly use N linkages with O linkages with Glu & galacotosami
• most things that have carbs -> glycosaminoglycans and mostly soluble. They often come soluble in white blood plasma(like cell fibers) and help in some bodies functions -> Cell surface glycoproteins are crucial for crosslinking and stableze the body -> they can use licen to attack diseases with synaptones(axon cell connection) via tromphin

Sugar facts

• many use glycoses for their function and are the bodies is the blood type, where in these cases they support the immunity where some of them have B or T
• The epthelial cells that bond cell form them on the surface where it is formed by glyctroproteins where it keeps the barrier for the cell

Gluconeogenesis

• a metabolic process which makes glucose with carbon substrats and is always present -- It's most common In the liver where you use certain resources, some is for energy.
• The pentose is another way, to get into cells and create glucose
• Gacaloctic gets reduced to convert by gaca kinase
• While glucose are compacted and they bond with fat to become fatty acid and form more fat or energy
• It makes fatty acid from carbs
• has many byproducts with what the body needs

Glycolisis

• A metabolic cycle that synthesizes glycogen. and breaks some of these cycles is due to bad cycles

List

• they are part of many medicines or just to help the body
• They can act as good agents
• has a good medium to cultures