Antigen Flashcards
Quiz 3
Where are integral membrane proteins and secreted proteins translated
into the ER (lumen (also how lysosomes are made)
What are three ways cells degrade proteins
-general proteases (housekeeping function)
-The proteasome (eukaryotes)
-autophagy (eukaryotes)
Explain how the cells degrade proteins with proteasomes
-the 26s Proteasome
-2 components with one that contain catalytic residues and one that determine access to catalytic site and unfold protein
How does the 26s Proteasome determine the catalytic residues
-proteins are marked by K48-linked Ub
-this leads to poly-Ub
-proteasome recognizes this and unwind protein and insert chain
What does proteasome generate
-small peptides
-these peptides are further degraded to AA
What is immunoproteasome
-isoform of the proteasome subunits that is used during inflammatory conditions
-uses IFN’s (anti-viral)
-prefers cleavage after hydrophobic residues
-leads to more MHC-I preferred peptides
What is thymoproteasome
-isoform of the proteasome subunit that is important for T-cell positive selection
-found in thymus
What is autophagy
-means “eat self”
-induces on stress/starvation
-also used for housekeeping
-generates peptides (MAIN POINT)
-“normal cell clean up”
What ar the three sources of antigens for “direct presentation”
-cytosolic pathogens (MHC I)
-Intravesicular pathogens (MHC II)
-extracellular pathogens and toxins (MHC II)
What problems does cross-presentation fix
-direct presentation only present MHC I meaning that the cells can’t move which is a problem if a virus only infects non-phagocytic cells
What is cross-presentation
-DC’s phagocytize virus-killed cell (contains viral antigens
-these antigens can be processed (degraded into peptides)
-loaded onto MHC-I (then DC moves to lymph nodes and activates naive T-cells
What is the difference between cross-presentation and direct presentation
-cross-presentation allows presentation of antigens from outside the cell on MHC I
-Direct presentation only allows antigen presentation from outside the cell on MHC-II
How do cytosolic peptides get to the ER
-Transporters associated with Antigen Processing (TAP)
-uses ATP tp pump peptides into ER
What if TAP’s imports 10-16 AA long peptides (this is too long)
-Endoplasmic Reticulum Aminopeptidase associated with Antigen Processing (ERAAP) trim AA to the right length
-TRIMS AA FROM N-TERMINUS
What does ERAAP tram from the M-terminus and not the C-terminus
-immunoproteasome cleaves C-terminus (hydrophobic)
What complex is formed once MHC-I is constructed
-Peptide-loading complex PLC
Describe peptide-binding releases MHC-I from the PLC
-prevents display of empty MHC-I
-prevents low-affinity peptide bind from display
What is the ey thing with MHC II
-prevent binding peptides until in the endosome
What is Ii
-invariant chain
-binds to MHC II to prevent incorrect peptide loading
tags MHC to the acidic endosomes
-cleaved, leaving the CLIP (CLass II-associated Invariant chain Peptide)
-eventually exchanges for a peptide
