chapter 7 Flashcards
Glycoproteins expressed on all nucleated cells: interact with Tc (CD8+ T ) cells
Class I MHC genes
Glycoproteins expressed APC cells: interact with TH (CD4+ T) cells.
Class II MHC genes
Secreted protein: complement and tumor necrosis factor (TNF)
Class III MHC genes
-Member of the Ig superfamily
-Larger 45 kDa glycoprotein α chain
-Smaller 12 kDa β2-microglobulin protein
-peptide binding groove between α1 and α2 domains
Class I molecules
-Member of the Ig superfamily
-Heterodimeric: 33 kDa α chain & 28 kDa β chain
-Both chains pass through the plasma membrane
-A peptide-binding cleft is formed by the pairing of the
α1 and β1 domains
class 2 molecules
occurs when two or more clearly different phenotypes
exist in the same population of a species
Polymorphism
Where do class I and class II molecules exhibit polymorphism?
in the peptide-binding region
How many class I and class II molecules can be expressed per person?
up to 6 class I and 12 class II
How does the limited group of molecules (class I & 2) present the vast diverse array of possible antigen peptide fragments?
A given MHC molecule can bind numerous different peptides, and some peptides can bind to several different MHC molecules
Describe the Class I MHC-peptide interactions:
-present peptides to CD8+ T cells
-some amino acids anchor the peptide into the groove
-other amino acids are available to interact with a TCR
Describe the Class II MHC-peptide interactions:
-present antigen peptides to CD4+ T cells
-some amino acids anchor the peptide into the groove
-other amino acids are available to interact with a TCR
What is the difference between class I and II regarding the nature of the peptide-binding groove?
MHC I is closed at both ends
MHC II is open at both ends
What is the size difference between class I and class II molecules?
class I is 8-10 amino acids
class II is 13-18 amino acids
describe the peptide motifs involved in binding to the MHC molecule for class I:
-anchor residues at both ends of peptide
-generally hydrophobic carboxyl-terminal anchor
describe the peptide motifs involved in binding to the MHC molecule for class II:
conserved residues distributed along the length of the peptide
describe the nature of bound peptide for class I:
extended structure in which both ends interact with MHC groove but middle arches up away from MHC molecule
describe the nature of bound peptide for class II:
extended structure that is held at a constant elevation above the floor of the MHC groove
describe the gene sequence of class I:
-5’ leader exon for signal peptide followed by 5–6 exons
encoding α chain
–Signal peptide is eventually removed
one of a number of alternative forms of the same gene or
same genetic locus (a group of genes)
allele