Glycoproteins Flashcards
Where are glycoproteins located?
Anchored to the extra cellular surface by lipid ceremide or a protein
Five locations of glycoproteins
Cell surface receptors Blood group determinants Collagen Fibronectin Protective barrier
What is unique about the structure of mucins?
Negatively charged sialic acid (NANA)
What is the function of mucins?
Occupy large space trap water act as protective barrier
What is unique about the structure of the oligosaccharide part of glycoproteins?
Mix of d-hexoses, NANA, and L-fucose (C6 has a methyl group)
What attaches the oligosaccharide to the protein?
Either an N-glycosidic link (through the amide group of asparagine) or o-glycosidic (OH group of Ser or Thr)
O linked oligosaccharides in glycophorin are linked to ser and thr by what?
linking protein is GalNAc (N-acetylgalactosine)
What is the characteristic disaccharide attached to hydroxylysine?
Glucose galactose
What are the two broad types of N-linked oligosaccharides
Complex oligosaccharides (GlcNAc, L-fucose, NANA) High mannose oligosaccharides (man)
What is the common structure in mammalian N linked oligosaccharides?
Linked to the amide nitrogen of Asn
Fuc Man
| / Asn--GlcNAC--GlcNAc--Man
\
Man
Where is the origin of the amine in UDP-Glucosamine?
Glutamine!
What is the final step?
CMP-NANA
What is the significance of NANA in the synthesis of glycoproteins?
When NANA is present oligosaccharide has a negative charge
Where does synthesis of o linked glycosides occur?
Protein made in rER and Glycosylated in golgi. Sugar added one at a time.
How does GLycosylation begin?
Transfer of GalNAc onto ser or thr OH group
How does synthesis of N-linked glycosides differ from O-linked?
Chain made separately in ER and attached to protein (instead of being added one at a time at Golgi)
Dolichol and dolichol phosphate are necessary!
What is the first step in biosynthesis of n-linked glycosides?
Protein synth in rER and enters lumen!
What is the second step of N-linked glycosides?
Lipid linked oligosaccharide made with dolichol attached through a pyro phosphate linkage to an oligosaccharide with GlcNAc mannose and glucose
What is the third step of N-linked glycoside biosynthesis?
Sugars added to dolichol by Membrane bound glycosyltransferases
What is the fourth step of N linked glycoside biosynthesis?
Oligosaccharide transferred to protein by protein oligosaccharide transferase (in ER)
5th step in n-linked glycoside biosynthesis?
Removal of specific mannosyl and glucosyl residues as glycoproteins moves through ER
6th step In biosynthesis of N-linked glycosides?
Completed in Golgi as either complex or high mannose
7th step of biosynthesis of N-linked glycosides?
Final processing
What is the inability to degrade GAGs or glycoproteins known as?
Mucoploysaccharidosis!
What is the inability to degrade sphingolipids known as?
Sphingolipidosis?
What targets n-linked glycoproteins for lysosomes?
Mannose 6 phosphate
What deficit is there in I cell disease?
Lack the ability to phosphorylate mannose residues
Lysosomal enzymes found in plasma (secreted instead of targeted)
