1. Exploring the Biological Roles of Glycans
Max Nanis

2. http://cardiovascres. oxfordjournals. org/content/83/2/388/F3. large

3. Principles & Conclusions about Biological Roles of Glycans
Range complete importance spectrum
Enormous diversity
Serve as a protein attachment surface
War of microbes is fought on a battlefield of carbohydrates!

5. Consequences of Altered Glycosylation Variate
Highly variable (intra class) - studied via:
Prevention of initial glycoslation
Alteration of oligosaccharide processing
Enzymatic or chemical deglycoslation of completed chains
Genetic elimination of glycosylation sites

6. Structural & Modulatory Roles
Protective, stabilizing, organizational, barrier functions, chaperonin
Modulate interaction with one another. GF receptors binding mechanism
Some specificity required by defined oligosaccharide sequence
Tuning: Heparin/heparan sulfate chains on anticoagulant antithrombin III, tyrosine phosphorylation acitivty of EGF receptor & insulin receptor

8. Specific Ligands for Exogenous Receptors
Extrinsic GBPs
Specific receptors for viruses, bacteria, parasites and symbiotic relationships
Some glycan sequences act as decoys for microoranisms and parasites
ex. Mucosal cell decoys with specific oligosaccharide ligand in mucin, then are washed away

9. Specific Ligands for Endogenous Receptors
Intrinsic GBPs
Earliest known mediated clearance, turnover and intracellular trafficking
Free oligosaccharides may induce highly structure-specific hormonal responses
Modern: cell- cell recognition, cell- matrix interactions
ex. Sperm:Egg binding via O-glycans

10. Homogeneous Glycans Can Have Different Roles
Expression of specific types of glycosylation of different glyconjugates in different tissues at different times of development implies these structures have diverse roles in similar organism.
New oligosaccharide or modification can evolve independently in different tissues and at a different time in development.

11. Universal Roles? Species-specific variation in glycan structure
Different selection pressures via pathogen exposure

12. Structure Variation
What components of glycans mediate essential biological roles?
Terminal sequences, modifications, and unusual structures

13. Determining Biological Roles
Structure and biosynthesis doesn’t imply understanding of function
Many functions discovered by chance
Difficult to differentiate between functions mediated by each glycan

15. Lectins / Antibodies
Lectins (sugar-binding proteins) and antibodies that are glycan specific
Localization (S35?)
Not reliable when introduced into systems where cross-creating glycan structures are potentially present (In vivo?)
Nonspecific aggregation

16. Lectins / Antibodies

17. Metabolic Inhibition or Alteration of Glycosylation
Pharmacological agents can inhibit glycosylation
Good to determine pathway
Con: May degrade membranes

18. Metabolic Inhibition or Alteration of Glycosylation

19. Natural Glycan Ligands:Specific Receptors
Promote potential lectin in high enough quantities, can look for specific ligands
Red cell agglutination, flow cytometry, surface plasmon resonance, and affinity chromatography
Con: Affinity of lectin for ligand may be low (need higher densities)

20. Natural Glycan Ligands:Specific Receptors

21. Receptors Recognizing Specific Glycans
Search for specific receptor
Hemagglutination, flow cytometry, and affinity chromatography
Reasonable quantities of purified glycan
Con: Lectin interactions can be low affinity, thus should use multivalent form of glycan
Most relevant receptor may be found in another organism!

22. Receptors Recognizing Specific Glycans

23. Interference by Soluble Glycans or Structural Mimics
SG or SM can interfere with interaction between lectin and glycan
Con: inhibitor cross-reacting with with unknown receptors

24. Interference by Soluble Glycans or Structural Mimics

25. Glycan Structure Elimination
Glycosidases are degradative and highly specific for certain glycan sequences
Does not interfere with biosynthetic machinery, but selectively eliminates structure (post synthesis)

26. Glycan Structure Elimination

27. Glycan Mutants
Con: defects in glycosylation may have limited/not easily discernable consequences
Often affect multiple systems/unpredictable phenotype
Redundant or fail-safe pathways possible
Best to analyze structural functions
Genetic defects relatively uncommon

28. Glycan Mutants

29. Receptor Mutants
Receptor alteration can yield informative phenotype in regards to function
Con: receptor protein my have unrelated functions to glycan recognition

30. Receptor Mutants

32. Functions
Protection: Cushions the plasma membrane and protects it from chemical injury
Immunity to infection: Enables the immune system to recognize and selectively attach foreign organisms
Defense again cancer: Changes in the glycocalyx of cancerous cells enable the immune system to recognize and destroy them

33. Functions
Transplant compatibility: Forms the basis for compatibility of blood transfusions, tissue grafts, and organ transplants
Cell adhesion: Binds cells together so that tissues do not fall apart
Inflammation regulation: Glycocalyx coating on endothelial walls in blood vessels prevents leukocytes from rolling/binding in healthy states

34. Functions Fertilization: Enables sperm to recognize and bind to eggs
Embryonic development: Guides embryonic cells to their destinations in the body