GLYCOPROTEINS Flashcards
A protein covalently linked to carbohydrates
glycoprotein
What types of glycosidic bonds are found in glycoproteins?
N-glycosidic, O-glycosidic, and glycosylphosphatidylinositol-anchored (glypiation)
Function of glycans in glycoproteins?
Cell signaling, recognition, stability, and folding.
Process of N-glycosylation?
Attachment of GlcNAc-PI to Asn residues.
Process of O-glycosylation?
Attachment of GalNAc to Ser/Thr residues
Impaired glycoprotein function due to defective glycosylation.
Congenital Disorders of Glycosylation (CDG)
What is glypiation?
Attachment of GPI anchor to C-terminal amino acids.
How does altered glycosylation contribute to cancer?
Changes in cell-cell interactions and receptor-ligand binding.
Role of glycoproteins in immunodeficiency?
Impaired immune response due to defective glycoprotein function.
Enzymes catalyzing glycosidic bond formation
glycosyltransferases
Enzymes catalyzing glycosidic bond hydrolysis.
glycosidases
Proteins binding specific glycans
lectins
What is the role of glycoproteins in protein stability?
Maintaining protein conformation and preventing degradation.
What is the role of glycoproteins in immune response?
Activating immune cells and mediating inflammation.
What is the role of glycoproteins in cell signaling?
Mediating cell-cell interactions and receptor-ligand binding.
enzyme responsible for N-glycosylation?
Oligosaccharyltransferase.
Enzymatic attachment of sugars to proteins
glycosylation
Nonenzymatic attachment of sugars to proteins
glycation
This process can have serious pathologic consequences
glycation
Often found in glycoproteins, attached to galactose, N-acetylglucosamine, or N-acetylgalactosamine
Sulfate
Can be used to purify glycoproteins
Lectins
Plant lectins were formerly called
Phytohemagglutinins
Common sugar in N-linked glycoproteins
Mannose
Present in both N-and O-linked glycoproteins
N-Acetylgalactosamine
An important red cell membrane glycoprotein that contains both O-and N-linked oligosaccharides
Glycophorin
Four subclasses of O-glycosidic linkages
N-acetylgalactosamine-Ser(Thr)
Proteoglycans
Collagen
Nuclear and cystolic proteins
The predominant linkage that found in mucins
N-acetylgalactosamine-Ser(Thr)
Contain a galactose-galactose-xylose trisaccharide attached to serine
Proteoglycans
Side chains consisting of single N-acetylglucosamine attached to serine or threonine residue
Nuclear and cystolic proteins
Contain galactose-hydroxy-lysine linkage
Collagen
Have a high content of O-linked Oligosaccharides
Mucins
Oligosaccharide branches are often referred as
Antennae
Biosynthesis of N-linked Glycoproteins involves
Dolichol-P-P-Oligosaccharides
These ensure correct folding of proteins in the endoplasmic reticulum
Glycoproteins & Calnexin
A chaperone protein in the ER membrane
Calnexin
Soluble ER protein that performs similar function to that calnexin
Calreticulin
3 Functions of GPI
Mobility
Signal transduction
target proteins
The overall series of reactions which involve in the browning of certain foodstuffs during storage or heating
Maillard reaction
Important in causing tissue damage in diabetes mellitus
Advanced glycation End-Products (AGEs)
