1. Glycosyltransferases and Glycosidases
TEST Next Thursday--only individuals signed up for a letter grade
Problem Set Hand Out Today--Will go over in class Tuesday
Also Tuesday--1st clinical correlation (Lance presenting)
- read papers BEFORE class & have 2 questions to hand in regarding the papers at the BEGINNING of class
Rearrangement of presenters
2nd clinical correlation paper will be posted before the weekend
Refresher of Tuesday’s lecture

2. newly synthesized
N-linked glycan
GlcNAc
Mannose
Glucose
Galactose
Sialic acid
Fucose

3. N-linked glycan synthesis: branching via GlcNAc addition
branch = antennae
GlcNAcT-III ß4
GlcNAcT-I ß2
GlcNAcT-II ß2
GlcNAcT-IV ß4
GlcNAcT-V ß6
GlcNAcT-VI ß4
GlcNAc
Mannose
Glucose
Galactose
Sialic acid
Fucose

5. Mechanisms of Glycosyltransferases
 Two main catalytic mechanisms
can be envisioned for glycosyltransferases :
inversion of the anomeric configuration
(for instance UDP-glucose -> b-glucoside)
or retention of the anomeric configuration
(for instance UDP-glucose -> a-glucoside).
glycosyltransferases (EC 2.4.x.y)
Core 3
GlcNAcT
Ser/Thr b3
Ser/Thr
UDP-GlcNAc
UDP
-most have divalent ion requirement and prefer neutral to acidic pH

6. Mammals utilize only 9 (?) sugar nucleotide donors for
glycosyltransferases: UDP-glucose, UDP-galactose,
UDP-GlcNAc, UDP-GalNAc, UDP-xylose, UDP-glucuronic
acid, GDP-mannose, GDP-fucose, and CMP-sialic acid.
Other organisms have an extensive range of sugar nucleotide
donors. Many glycosyltransferases in higher and lower
organisms use lipid linked glycosyl donors where the
lipid is frequently a terpenoid such as dolichol or polyprenol.

7. STRUCTURE OF GLYCOSYLTRANSFERASES
--vast majority fall into 3 types of folds
-- CAZy ~ Carbohydrate-Active enZymes
glycosyltransferases into over 86 families
(structure, mechanism, substrate, acceptor)

8. Type II Transmembrane Proteins
--couple of exceptions in Man-6-P
lysosomal targeting pathway

9. Many Transferases are Expressed in Soluble Forms and/or
Processed and Secreted-----Why?????

10. Strict acceptor substrate requirements
One-linkage-one-enzyme paradigm

11. Exceptions to the Paradigm
Specific linkage can be product of several related gene products (2-8 sialytransferase family)
Rarely a glycosyltransferase can synthesize 2 different linkages (FucT-III 1-3 and 1-4)
Acceptor specificity modulation (GlcNAc to Glc for b4-galactosyltransferase by lactalbumin)
Glycosyltransferase that catalze two stepwise reactions (copolymerases of GAG chains)

12. Glycosidases Two Mechanisms--inverting/retention
Very Diverse in Primary and Tertiary Structure
Most localized to lysosome

13. Retention of Configuration (EC 3.2.1.-)

14. Inversion of Configuration

15. Degradation of N-linked
Proteins--both reducing
& non-reducing end
degradations

17. Glycosphingolipid Degradation
-terminal in lysosomes
-some cleavages require SAPs (sphingolipid activator proteins)

19. Non-reducing end degradation
HA Degradation
Non-reducing end degradation

20. Degradation of Heparan Sulfate
Non-reducing end degradation

21. Keratan Sulfate Degradation
Non-reducing end breakdown

23. For the Test Next Week Read Essentials and Go Over Presentations
Nomenclature (Three letter glycans, linkage, etc..)
Major Types of Glycosylation
(N-linked, O-linked, Lipid linked, Proteoglycans)