Chapter 7: Polysaccharides as Informational Molecules

What are lectins

Carbohydrate binding proteins (CHO are the ligands for lectins)

What do surface carbohydrates and lectins mediate?

1. Cell to cell communication

2. Differentiation of cells

3. Cellular ECM

4. Pathogen-cell interactions

5. Intracellular trafficking

The antigens on human RBCs are…

Oligosaccharides!

What are the different blood type antigens?

O, A, B

What’s the monomer sequence of the O, A and B antigens?

What blood type can receive from all other blood types?

AB

Why do people with O type blood experience less severe cases of malaria?

The RBCs clump together less; less “rosetting”

Which blood type is more liable to more severe cholera?

Type O

How does Norovirus infect its host?

Binds to ABO sugars

What is sialic acid? What’s its function?

• 9 Carbon amino sugar

• Usually connected to a glycoprotein on a Ser residue on RBCs → most abundant oligo on RBCs

• Ensures that RBCs don’t clump together bc it makes them highly negatively charged

• Also serves as an age marker for RBCs → sialic acid is slowly degraded as it circulates in our blood stream

Lectins can aide in cell specific ___

Aggregation

Explain the lectin sponge experiment

Grinded up sponge re-aggregates with itself over time. The red and blue sponges had different oligosaccharides

CHOs are also important in…

Embryogenesis- 8 cell phase, specific kinds of CHOs being presented on the surface of cells

Leukocytes (white blood cells) must __ circulation to fight infections

Leave

Describe the process of leukocyte homing

• On the endothelial cell surface, there are lots of receptor molecules, such as p-selectin

• On the leukocyte, glycoproteins, ligands for p-selectin, and integrin are present on the surface

  • Integrins are adhesion proteins

• The leukocyte’s oligosaccharides first binds to the lectin receptors on the endothelial surface, and it “rolls” along the surface

• The integrin ligands and lectins become more dense near the site of inflammation so that the leukocyte rolls to a stop and be sequestered into the site of infection

What are selectins?

Family of plasma membrane lectins that mediate cell-cell recognition and adhesion

What are the 3 different types of selectins?

1. E: induced in inflammation, on endothelium

2. L: expressed on leukocytes, homing to lymph nodes

3. P: On platelets and endothelium

Integrins are not __or __

selectinsor lectins

What are integrins

Transmembrane receptors

How are integrins activated (usually inactive, must be pointed up)

By signals in inflamed tissues

Sperm has a receptor complex that can recognize the ___glycoprotein sugar on the __ ___ on the egg cell

ZP3, Zona pellucida

The CHO surface of cancer cells is __ than healthy cells

dramatically different, they dont sense that there’s too many of them

Pathogens bind to host cells via…

Lectin/CHO binding interactions

Bacteria can recognize CHO on the surface of __ cells to infect

Intestinal

Ex: H. Pylori

Cholera toxin is a ___

Lectin

How does cholera toxin induce illness

Binds to glycolipid(GM1) in the intestine, which activates the chloride pump, which leads to the flooding of the intestine with water and ultimately diarrhea

Explain the significance of the Giardia lamblia parasite

It can survive our stomach acid and when it enters the intestine its lectin, a taglin, is activated by trypsin

Explain the significance of Entamoeba histolytic

Binds to the CHOs on human cell surfaces and eats up our cells

What particle does the influenza virus recognize on our cell surfaces

Sialic acid

What is the viral lectins named for influenza

Haemagglutinin protein (HA)