Epitopes Flashcards
What is the actual binding site of an antigen?
Epitopes
Do lymphocytes recognize entire antigens?
No, they recognize small, discrete sites
What is an epitope?
Small, discrete site on macromolecules
Antigenic determinants
Epitopes
How do B-cell epitopes bind AG
B-cells bind Ag directly via cell surface immunoglobulin
What can Ag be for B-cells?
Almost anything
For Ag in solution for B-cells what three things must the epitopes be?
- Topographically accessible (outside surface)
- Flexible and mobile
- Sequential or conformational (nonsequential)
What is a conformational epitope?
Nonsequential
Distinct entities that fold together
How is the epitope size defined?
Defined by the binding site of the antibody
Lock and key fit
What limits epitope size?
Complimentary binding between Ag-Ab
What can hold more aa? Conformational or linear
Conformational epitopes cover much greater space on flatter surface binding sites of Ab
Can hold 15-22 aa
Do all epitopes induce a response?
No, there is immunodominance
How many aa can typically fit in a linear epitope binding site?
6-7 aa or sugars
What are the four shapes of epitopes for B cells?
- Hot dog in bun
- Semi-circle
- Sphere
If I stretch out a conformational epitope will it work?
No, it needs to be in a 3D shape
Linear
sequential
Conformational
Non-sequential
Can we denature and digest a linear epitope?
Yes
Can we denature and digest a conformational epitope?
No
What do T-cell epitopes see?
Only peptides
Can a T-cell recognize soluble native Ag
No
Can a T-cell bump into something and recognize it?
No, it needs to be instructed
How does a T-cell recognize Ag?
The Ag has to be processed and whole peptide fragments are presented in association with MHC molecules
MHC
Major Histocompatibility Complex
Oligomer
“few parts”
T-cell epitopes are oligomeric peptides of how many aa?
7-20 aa
MHC class 1 is how many aa?
9-11 aa
What does MHC 1 do?
Shows peptides to killer T-cells
How many aa is MHC class 2?
11-17 aa
What does MHC 2 do?
Shows peptides to helper T-cells
What is required to generate peptides?
Ag processing
Ag is seen as part of a trimolecular complex. What are the 3 parts?
TCR (tcell receptor)
Ag
MHC
Peptides must be amphipathic. What two regions do they need?
Hydrophilic - TCR
Hydrophobic - MHC
Hydrophobic
MHC
Hydrophilic
TCR
What does the TCR recognize?
MHC and peptide
Agretope
MHC binding site of the Ag
How do agretope sites bind?
Via hydrophobic aa
Epitope
TCR binding site
How do epitope sites bind?
Hydrophilic aa
How are immunodominant T-cell epitopes determined?
By what set of MHC molecules are expressed and what TCR are expressed
