glycoproteins
DESCRIPTION
GLYCOPROTEINS. Dr Amina Tariq Biochemistry . Glycoproteins. Glycoproteins are proteins that contain oligosaccharide ( glycan ) chains covalently attached to their polypeptide backbones. Almost all the plasma proteins of humans—except albumin—are glycoproteins . - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/1.jpg)
GLYCOPROTEINSDr Amina TariqBiochemistry
![Page 2: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/2.jpg)
GlycoproteinsGlycoproteins are proteins
that contain oligosaccharide (glycan) chains covalently attached to their polypeptide backbones.
![Page 3: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/3.jpg)
Almost all the plasma proteins of humans—except albumin—are glycoproteins.
Many proteins of cellular membranes contain substantial amounts of carbohydrate.
![Page 4: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/4.jpg)
A number of the blood group substances are glycoproteins.
Certain hormones (eg, chorionic gonadotropin) are glycoproteins.
![Page 5: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/5.jpg)
They differ from proteoglycans:1. Length of the chain is relatively
short (usually 2-10 sugar residues) very long in GAGs.
2. Do not have repeating disaccharide units.
3. They are branched.4. May or may not be negatively
charged.
![Page 6: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/6.jpg)
Glycoproteins occur in most organisms, from bacteria to humans.
Their carbohydrate content ranges from 1% to over 85% by weight.
They perform the following functions:
![Page 7: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/7.jpg)
Function ExampleStructural role CollagenTransport role TransferrinImmunologic role ImmunoglobulinsCell-to-cell communication
SelectinsProteins in fertilizationCell adhesion molecules
Cell signalling Many receptorsClotting Plasma proteins
LipoproteinsLubrication Mucins
![Page 8: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/8.jpg)
Hormones HCG, TSH Anti freeze cold water fish
![Page 9: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/9.jpg)
Some of the processes involving glycoproteins:
inflammation blood clotting peptic ulcers AIDS (HIV)
![Page 10: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/10.jpg)
influenza fertilization cancer cystic fibrosis arthritis
![Page 11: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/11.jpg)
![Page 12: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/12.jpg)
![Page 13: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/13.jpg)
The predominant sugars found in glycoproteins are:
glucose (Glc), galactose (Gal), mannose (Man), fucose (Fuc),
![Page 14: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/14.jpg)
N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc) and N-acetylneuraminic acid
(NANA). NANA is also called sialic acid.
![Page 15: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/15.jpg)
The distinction between proteoglycans and glycoproteins resides in the level and types of carbohydrate modification.
![Page 16: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/16.jpg)
Proteoglycans also contain the sugar glucuronic acid (GlcA).
The carbohydrate modifications found in glycoproteins are rarely as complex as that of proteoglycans.
![Page 17: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/17.jpg)
The carbohydrates of glycoproteins are linked to the protein component through either O-glycosidic or N-glycosidic bonds.
![Page 18: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/18.jpg)
The N-glycosidic linkage is through the amide group of asparagine (Asn, N).
The O-glycosidic linkage is to the hydroxyl of serine (Ser, S), threonine (Thr, T) or hydroxylysine (hLys).
![Page 19: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/19.jpg)
O-linked sugars:May be membrane glycoprotein
componentsOr extracellular glycoproteins.
![Page 20: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/20.jpg)
When attached to Ser or Thr, the sugar of O-linked glycoproteins is most often GalNAc.
![Page 21: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/21.jpg)
N-linked sugars: The predominant carbohydrate attachment in glycoproteins of mammalian cells is via N-glycosidic linkage.
![Page 22: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/22.jpg)
They are of two types:1. Complex oligosaccharides2. High mannose oligosaccharides
![Page 23: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/23.jpg)
Their core pentasaccharide is the same.
In the complex form additional sugar residues are present:
N-acetylglucosamine (GlcNAc) and N-acetylneuraminic acid
(NANA). Fucose
![Page 24: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/24.jpg)
High mannose contain only mannose residues
![Page 25: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/25.jpg)
Most proteins that are secreted, or bound to the plasma membrane, are modified by carbohydrate attachment.
The part that is modified, in plasma membrane-bound proteins, is the extracellular portion of the protein.
![Page 26: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/26.jpg)
Intracellular proteins are less frequently modified by carbohydrate attachment. However, the attachment of carbohydrate to intracellular proteins confers unique functional activities on these proteins
![Page 27: GLYCOPROTEINS](https://reader035.vdocuments.site/reader035/viewer/2022070422/568163a7550346895dd4b23b/html5/thumbnails/27.jpg)
I – cell diseaseCancers Metastasis