Essentials of Glycobiology

May 5th., 2008

Ajit Varki

Lecture 12

Chapter 13. Sequences Common to Different Glycan Classes

Chapter 33. Galectins

Major Glycan Classes in Vertebrate Cells

Shared Terminii in Different Glycan Classes of Vertebrate Cells

Essentials Second Edition Symbols

General Questions for Lecture 111. Propose a function for the allelic variation observed in the ABO blood group system. If

non-primates do not express the ABO locus due to evolutionary loss of the gene, how would this affect your answer?

2. Hyperacute (graft) rejection occurs after transplantation of organs from non-human donors into humans and results from an immediate reaction of circulating anti-GalGal antibodies with the transplanted tissue. Suggests ways to modify the donor or acceptor to prevent HAR.

3. Compare and contrast "LacNAc" and "LacdiNAc" units. How does the presence of these terminal disaccharides affect the addition of sialic acid and fucose?

4. Based on what you know about terminal structures on FSH and LH, propose several glycan-based mechanisms that could account for infertility in humans.

5. Certain strains of E. coli bind to P-blood group antigens and cause urinary tract infections. What evolutionary advantage might exist for retaining the transferases for a deleterious glycan?

6. Why do changes in glycan branching pathways and sialylation have the potential to impact galectin function?

7. How do galectins achieve high-affinity binding to cell surface glycans?

8. How do you explain the finding that galectins are not routinely found in large amounts in body fluids, even though they are soluble secreted proteins?

9. Explain how a galectin could act as a receptor for microbial infection

10. How do galectins send signals through cell surface receptors?

FIGURE 13.2. Terminal GlcNAc residues are usually galactosylated in Vertebrate Cells

3. Compare and contrast "LacNAc" and "LacdiNAc" units

"LacNAc"

FIGURE 13.3. Poly-N-acetyllactosamine chains are found on N-glycans, O-glycans, and glycolipids

“Polyllactosamine” Chains

N-acetyllactosamine

Unit

FIGURE 13.4. i and I antigen synthesis

Embryonic

AdultCold-dependent agglutinating antibodies

(cold agglutinins) in patients withacquired hemolytic anemia (see Chapter 43). Cold agglutinin antibodies react with

red blood cells of most blood donorsIncluding patient’s own cells!

FIGURE 13.5. Type-1 and -2 H, A, and B antigens that form the O (H), A, and B blood group determinants on N- and O-glycans

“O” “A” “B”

FIGURE 13.8. Synthesis of H (O), A, and B blood group determinants

“O”

“A”

“B”Anti-A

Anti- B Anti-A

Anti-B

“AB”

NoAntibodies

“Universal Donor”

“Universal Acceptor”

O-glycans

Glycosphingolipids

FIGURE 13.10. Type-1 and -2 Lewis determinants

3. How does the presence of terminal disaccharides affect the addition of sialic acid and fucose?

Some of these are Ligands for

Selectins

Type-1 Lewis blood group determinants on glycoproteins

and glycolipids (R) are characterized by the presence or

absence of the Secretor locus α1-2FucT and the Lewis locus

α1-3/α1-4FucT.

FIGURE 13.11. Lewis blood groups based on Type 1 LacNAc

3. Propose a function for the allelic variation in the ABO blood group system. If non-primates do not express the ABO locus due to evolutionary loss of the gene, how would this affect answer?

“O”

“A”

“B”Anti-A

Anti- B Anti-A

Anti-B

“AB”

NoAntibodies

FIGURE 13.12. Biosynthesis of antigens of the P blood group system: Pk, P, and P1.

5. Certain strains of E. coli bind to P-blood group antigens and cause urinary tract infections. What evolutionary advantage might exist for retaining transferases for a deleterious glycan?

E.coli

E.coli

Parvovirus B19

Alpha-Gal Epitope Anti-alpha Gal Antibodies

Owl Word Monkeys Apes & Humans - +Other Mammals + -

2. Hyperacute (graft) rejection occurs after transplantation of organs from non-human donors into humans and results from an immediate reaction of circulating anti-GalGal antibodies with the transplanted tissue. Suggests ways to modify the donor or acceptor to prevent HAR.

FIGURE 13.15. Structure and synthesis of N-glycans bearing terminal N-acetylgalactosamine (GalNAc), including sulfated GalNAc on pituitary hormones lutropin (LH) and thyrotropin (TSH).

4. Based on what you know about terminal structures on FSH and LH, propose several glycan-based mechanisms that could account for infertility in humans.

3. Compare and contrast "LacNAc"

and "LacdiNAc" units

"LacNAc""LacdiNAc"

FIGURE 13.16. Synthesis of the human Sda or mouse CT antigen and the glycolipid GM2

FIGURE 13.17. Synthesis of glycoproteins and glycolipids bearing terminal α2-3 sialic acid transferred by the ST3Gal family of sialyltransferases

FIGURE 13.18. Synthesis of α2-6 sialic acids (see Chapters 9 and 10)

TumorAntigen

Cosmc

FIGURE 13.19. Structure and synthesis of polysialic acid on N-glycans

Embryonic

Adult

NeuralPlasticity

FIGURE 13.20. Structure and synthesis of polysialic acid on glycolipids.

NeuralFunctions?

CD57 NK cell MarkerAntigen in Myeloma

P0 Ligand?Cellular Interactions

FIGURE 13.22. Synthesis of keratan sulfate. Different 6-O-sulfotransferases (SulfoT) transfer sulfate to 6-position of Gal and GlcNAc in poly-N-acetyllactosamine chains.

KS is attached to proteins (R) via an N-glycan (KS type I) or an O-glycan (KS type II).

Human Macular Corneal Dystrophy

Is Ks and Glycosaminoglycan (GAG)?

FIGURE 33.3. (a) Ribbon diagram of crystal structure of human galectin-1, complexed with lactose. Homodimer shown with each monomer colored differently and orthogonal views are presented. The subunit interface is based on interactions between the carboxy- and amino-terminal domains of each subunit.

(c) Primary sequence of human galectin-1 with the numbered residues corresponding tothose highlighted in the crystal structure above.

(b) Interactions between key amino acid residues within the CRD of galectin-1 when lactose is bound (left panel) and when no sugar is bound(right panel).

7. How do galectins achieve high-affinity binding to cell surface glycans?

8.How do you explain the finding that galectins are not routinely found in large amounts in body fluids, even though they are soluble secreted proteins?

FIGURE 33.2. Possible biosynthetic routes for galectins in animal cells.

FIGURE 33.4. Functional interactions of galectins with cell-surface glycoconjugates and extracellular glycoconjugates can lead to cell adhesion and signaling. Interactions with intracellular ligands may also contribute to regulation of intracellular pathways.

10.How do galectins send signals through cell surface receptors?

FIGURE 33.5. A list of known and putative functions and biological activities of galectins toward cells in the immune system.

General Questions for Lecture 111. Propose a function for the allelic variation observed in the ABO blood group system. If non-primates do not express

the ABO locus due to evolutionary loss of the gene, how would this affect your answer?

2. Hyperacute (graft) rejection occurs after transplantation of organs from non-human donors into humans and results from an immediate reaction of circulating anti-GalGal antibodies with the transplanted tissue. Suggests ways to modify the donor or acceptor to prevent HAR.

3. Compare and contrast "LacNAc" and "LacdiNAc" units. How does the presence of these terminal disaccharides affect the addition of sialic acid and fucose?

4. Based on what you know about terminal structures on FSH and LH, propose several glycan-based mechanisms that could account for infertility in humans.

5. Certain strains of E. coli bind to P-blood group antigens and cause urinary tract infections. What evolutionary advantage might exist for retaining the transferases for a deleterious glycan?

6. Why do changes in glycan branching pathways and sialylation have the potential to impact galectin function?

7. How do galectins achieve high-affinity binding to cell surface glycans?

8. How do you explain the finding that galectins are not routinely found in large amounts in body fluids, even though they are soluble secreted proteins?

9. Explain how a galectin could act as a receptor for microbial infection

10. How do galectins send signals through cell surface receptors?