Antibodies genetics and structure Flashcards
What is the Ab molecule made of?
Glycoprotein
2 heavy chains (V+C), 2 light (V+C)
What are hypervariable regions?
3 regions on H and 3 regions on L. CDR1,2,3
AA on CDR complements AA on Ag
How many different heavy chains are there? (names)
How many different light chains?
9 different heavy : IgG1-4, IgA 1-2, IgD, IgE, IgM
2 dif light: kappa or lamda
How does variability of constant region come about?
When Ig genes recombine
Genes on human heavy chain locus are:
How are they organised
38-46 VH genes, 27 DH genes, 6 JH genes
Organised in clusters upstream of constant regions
Genes on human lamda locus
30 V lamda genes, five J lamda, each J lamda followed by constant segment
Genes on human kappa locus:
34-40 Vkappa genes and 5 J kappa genes, J upstream of constant
Describe genetic recomb:
When HPSC differentiates to B cell - start to recombine Ig gene
1- pick 1/27 D and put it next to J, cut loop
2- pick 1/40 V and put it next to DJ, cut loop
3- Then still everything between VDJ and C is still there - when transcripted to mRNA, splice out bits in between
CDR 1, 2, 3 bits:
CDR 1 and 2 - only V
CDR 3 - VDJ
How do you recombine LC?
Same way, start kappa, if not successful, do lamda
Chances at Ig Building
1 set of genes from mom, one set from dad. So 2 chances at HC, and 4 at LC
How much variability due to genetic recombination?
1.3x10^6 + additional
What is VDJ recomb mediated by?
Recombinase enzyme coded by RAG 1 and 2 recognising RSS on nucleotides flanking VDJ.
Structure and Types of RSS, why?
Both heptomer space nanomer
Heptomer and nanomer sequence and length conserved
Space length conserved either 12 or 23
12 can only recombine with 23 - so 1 V, 1 D, 1 J
4 ways to get additional diversity:
- exact location of splice isn’t set so inaccuracies
- N-nucleotide addition by TDT before religation
- Chain combinations
- Somatic hypermutation (point mutations)
Upto how many different antibodies can we get?
10^15
How and when do you class switch?
So first, heavy chain recombines VDJ, then makes IgM
then class switch
eg c mue to c epsilon looped out
Are RSS used in class switching?
No, switch sequence is upstream of enzyme for each C, and different enzyme is used too
Why does Naive B cell make both IgM and IgD?
Only one switch seq before mue, non before delta
How are antibodies flexible?
Have hinge regions at their neck
Can antibodies make polymers? explain:
Secretory IgA is a dimer, circ monomer
Circ IgM is pentamer, cell surface monomer
