Lecture 8: Antigen Processing

Question 1

What are the 2 great domains of the cell?

Answer 1

• Cytoplasm & contiguous structures
• Intracellular vesicles and organelles

Question 2

What do CD8 T cells recognise?

Answer 2

CD8 T cells recognise class I molecules that bind peptides from the cytoplasm and contiguous structures like the nucleus

Question 3

What is ubiquitin?

Answer 3

A ubiquitous cytosolic protein that ends in cysteine, which can be covalently bound to a lysine

Question 4

What is the main function of ubiquitin?

Answer 4

Tagging proteins for degradation by the proteasome

Question 5

What is ubiquitin ligation useful for?

Answer 5

Protein degradation, signal transduction, cell death protection and DNA repair

Answer 6

• ubiquitin tagged proteins are necessary for most proteins to be protealised by the proteasome

Question 7

What is the proteasome?

Answer 7

The major proteolytic system in the cytoplasm that makes things ordered

Question 8

What does the proteasome structure consist of?

Answer 8

barrel shaped with 4 rings, each ring has 7 members,
2 alpha rings: gates on the outside
2 beta rings: in the middle containing 3 threonine proteases

Question 9

What are the 3 different proteasome types?

Answer 9

Constitutive proteasome, immnoproteasome, adnd thymoproteasome

Question 10

What is the immunoproteasome?

Answer 10

• subunits have been induced by gamma interferon (Beta1i/2i/5i)
• makes c-terminus of the peptide better for the class I molecules that the peptides are directed towards
• turned on by inflammation

Question 11

How does IFNy effect the immunoproteasome?

Answer 11

Stimulates better antigen presentation, as it up regulates MHC I and MHC II presentation

Question 12

What cells express the thymoproteasome?

Answer 12

Expressed in cTECs for better positive selection

Question 13

What is the difference between cytoplasm and cytosol?

Answer 13

Cytosol has organelles, cytoplasm is without

Question 14

What to cytosolic proteases do?

Answer 14

Trim peptides after proteasome degradation

Question 15

What is TAP?

Answer 15

Transporter for antigen presentation is a typical ATP-binding cassette (ABC)

Question 16

What are TAP1/2 composed of?

Answer 16

Each composed of a Tapasin-binding domain, a transmembrane (TM) peptide-binding domain, and a nucleotide binding domain (NDB)

Question 17

How is the ATP site of TAPs arranged?

Answer 17

Each ATP binding site is split between the NDBs of TAP1 and TAP2, so both must come together to hydrolyse one ATP

Answer 18

• the C-terminal specificity of the TAP corresponds with the specificity of the class I molecule at pocket F
• the immunoproteasome produces peptides that fit the specificity of the class I molecule at pocket F
• there is not much specificity for the N terminus of peptides that are transported hence the N-terminus may be adjusted by amino peptidases in the ER (ERAPs)

Question 19

What is pocket F?

Answer 19

C-terminal specificity of the TAP corresponds with the specificity of class I molecules in pocket F (where the C terminal of amino acids go)

Answer 20

There is no specificity for the N terminus, so has to be adjusted by ER animo peptidases (ERAPs)

Question 20

What are the first steps of antigen presentation pathway in class I molecules?

Answer 20

• translation of class I heavy chain into the ER lumen, with co-translational N-linked glycosylation
• heavy chain binds to chaperone calnexin, with glucosidases trimming N-linked glycan
• heavy chain loses calnexin and binds ß2 micro globulin
• immature class I molecule without the peptide binds chaperone Tapasin which then binds TAP