Glycoproteins and Lectins

Question 1

Why would we attach a carb to a protein?

Answer 1

Many cell-cell interactions are driven by carbohydrate/protein binding

Question 2

O-linked glycosylation

Answer 2

Carbs attach to side chain hydroxyl oxygen of Serine and Threonine

Question 3

N-linked glycosylation

Answer 3

Carbs attach to side chain amide nitrogen of asparaginw

Question 4

What are the 4 features of Carbs that make them info rich?

Answer 4

1. Diverse monosachharide
2. Varying asometric states (a and b)
3. Diff. glycosidic linkages (alpha 1,4 beta 1,4 and alpha 1,6)
4. diff glycosidic linkages to protein (O or N-linked)

Question 5

What are the 2 ways that glycosylation changes the properties of protein?

Answer 5

1. Provides surface for interactions w/ other proteins

2. may change functions too

Question 6

What are the 3 classes of glycoproteins?

Answer 6

Glycoprotein
Proteoglycans
Mucins

Question 7

Glycoprotein

Answer 7

Protein>carb (by weight)

Question 8

Carb>protein

Answer 8

Proteoglycans

Mucins

Question 9

Describe Erythropoietin

Answer 9

Hormone that stimulates RBC production

3 N-linked
1 O-linked

40% carb (so glycoprotein)
Enhances stability

Question 10

Proteoglycans

Answer 10

More carb than protein

Lubricants and structural components in connective tissue, adhesion of cells to extracellular matrix

Question 11

What are proteoglycans attached to?

Answer 11

Glycosaminoglycans

Question 12

Glycosaminoglycans

Answer 12

repeating unit chemically modified to have negative roots

Question 13

What is agrecan

Answer 13

A proteoglycan found in cartilage

Question 14

What are mucins?

Answer 14

Glycoprotein components of mucus

Question 15

VNTR

Answer 15

Variable number of tandem repeats

Question 16

What are the functions of mucins

Answer 16

Act as a lubricant in saliva

Protective barrier when adhered to epithelial cells (line of lungs, stomach, eyes)

Question 17

Glycoprotein
main features
Example/function

Answer 17

more protein than carb
N- or O-linked
EPO glycosylation improves stability stability of protein in blood

Question 18

Proteoglycan

Answer 18

Carb>protein
Attached to glycosaminoglycans
Aggrecan found in cartilage
Glycosaminoglycans have neg. charge that absorbs water (cushion)

Question 19

Mucin

Answer 19

Carb>protein
Extensive O-linked glycosylation in VNTR
MUC2/ glycans bind water, form gel, lubricate and protect intestinal tract

Question 20

Lectins

Answer 20

Proteins that bind carbs

Question 21

Selectins

Answer 21

Class of Lectins that help immune system bind to sites of injury
Bind to carbs on diff surfaces

Question 22

L-selectin

Answer 22

Binds carbs on lymph-node vessels

Question 23

P-selectin

Answer 23

Binds carbs on activated blood platelets

Question 24

E-selectin

Answer 24

Binds carbs on endothelium