Glycoproteins and peptidoglycans

1
Glycoproteins and peptidoglycans

• ????? ???????????????
• ?????????????????????
• ?????????????? ??????????????????

2
????????????

• ?????????????? ???????????????????????????????????
  ???????????
• ??????????????????????????????????????????
• ??????????????? ??????????????????????????????????
  ???????????????

3
Glycoconjugates

• Glycoproteins
• Proteoglycans Glycosaminoglycans (GAGs)
• Glycolipids

4
Glycoproteins

• Oligosaccharides or glycan--gtprotein covalent
  bond

5
Some Biological Functions of Glycoproteins

• ??????? ???????????????
• Structural molecule Collagens
• Lubricant and protective agent Mucins
• Transport molecule Transferrin, ceroluplasmin
• Immunologic molecule Immunoglobins,
  histocompatibility antigens
• Hormone Chorionic gonadotropin,
• thyroid-stimulating hormone (TSH)
• Enzyme Various, eg. alkaline phosphatase
• Cell attachment recognition site Various proteins
  involved in cell-cell (eg.
• Sperm-oocyte), virus-cell, bacterium-cell,
  and
• hormone-cell interactions
• Antifreeze Certain plasma proteins of cold
  water fish
• Interact with specific carbohydrates Some lectins

6
Some Functions of Glycan in Glycoproteins

• Modulate physiochemical properties, eg.
  Solubility, viscosity, charge, and denaturation
• Protect against proteolysis, from inside and
  outside of cell
• Affect proteolytic processing of precursor
  proteins to smaller products
• Are involved in biological activity, eg. of
  human chorionic gonadotropin (hCG)
• Affect insertion into membranes, intracellular
  migration, sorting and secretion
• Affect embryonic development and differentiation
• May affect sites of metastases selected by
  cancer cells

7
???????????????? glycoproteins

• Galactose
• Glucose
• Mannose
• Fucose
• Xylose

• N-acetylneuraminic acid
• N-acetylgalactosamine
• N-acetylglucosamine

8
Protein-carbohydrate linkages
9
Protein-carbohydrate linkagesN-linked
glycoproteins
10
Protein-carbohydrate linkagesglycosylphosphatidyl
inositol, GPI linked glycoprotein
11
Mucin

• Glycoproteins O-linked oligosaccharides
  ????????? (gt50)
• ??????? ???? repeating amino acid sequence
  (tandem repeat)

O-glycan chain
N-glycan chain
Tandem repeat seq
C-teiminus
N-teiminus
12
Mucus

• ??? 94 mucin 5
• 1 cell debris, others

13
Glycoprotein and inflammation
14
Role of glycoprotein in attachment recognition
15
Proteoglycans and glycosaminoglycans

• Mucopolysaccharides
• core protein GAGs

Trisaccharide bridge
Ser
(GlcA-gtGalNAc)n-gtGlcA
Gal-gtGal-gtXyl
Chondroitin sulfate
Core protein
16
Proteoglycan structure of an integral membrane
protein
17
Structure of GAGs
18
Structure of proteoglycan
19
Structure of proteoglycan
20
Mucopolysaccharidoses