antibody diversity. structure of immunoglobulins/antibodies complement activation binding to cells...
TRANSCRIPT
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ANTIBODY DIVERSITY
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s
s
s
s
s
s
s
s
s ss s
CH2
CH3
s
s
s
s
s
s
s
s
ss
VL
VH
CL
CH1 ss
ss
s
s
s
s
ss
effektor funkciók
konstans domének
antigénkötés
variábilis domének
STRUCTURE OF IMMUNOGLOBULINS/ANTIBODIES
SS
COMPLEMENT ACTIVATION
BINDING TO CELLS
DEGRADATION
TRANSPORT
Light chain (L)
Heavy chain (H)
VL
CL
VH
CH
Antigen binding
Variable domains
Antigen
Constans domains
Effector functions
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MMultiple myeloma (MM)ultiple myeloma (MM)PPlasmlasmaa cell tumors – tumor cells reside in cell tumors – tumor cells reside in tthe bone marrowhe bone marrowProduce immunoglobulins of monoclonal origin,Produce immunoglobulins of monoclonal origin, serum concentration 50-100mg/mlserum concentration 50-100mg/mlRodney Porter & Gerald Edelman 1959 – 1960Rodney Porter & Gerald Edelman 1959 – 1960 myeloma protein purification myeloma protein purification
AMINO ACID SEQUENCE OF IMMUNOGLOBULINS
50 kDa50 kDaHeavy chainHeavy chain
25 kDa25 kDaLight chain Light chain
Gel electrophoresisGel electrophoresis
Variable Constant
123456789101112131415161718
Reduction
L H
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GENETIC BACKGROUND OF ANTIBODY DIVERSITY
VLVLVHVH
Mechanism of the generation of variability?Different rules for encoding the variable and constant regions?
S – S S – S
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MMany GENEany GENESS (10 (10 000 – 000 – 3300 000)000)
VV22 CC22 VVnn CCnnVV11 CC11
1 GEN1 GEN
HHigh rate of somatic mutations in igh rate of somatic mutations in tthe he VV-region-region
VV CC
GGeenn
ProteinProtein
1 G1 GENEN = 1 = 1 PROTEIN PROTEIN
DOGMA OF MOLECULAR BIOLOGY
CHARACTERISTICS OF IMMUNOGLOBULIN SEQUENCE
THEORIES
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MOLECULAR GENETICS OF IMMUNOGLOUBLINS
• A single C region gene encoded in the GERMLINE and separate from the V region genes
• Multiple choices of V region genes available• A mechanism to rearrange V and C genes in the genome so that they can
fuse to form a complete Immunoglobulin gene.
In 1965, Dreyer & Bennett proposed that for a single isotype of antibody there may be:
How can the bifunctional nature of antibodies be explained genetically?
This was genetic heresy as it violated the then accepted notion that DNA was identical in every cell of an individual
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The Dreyer - Bennett hypothesis
VV
VV
V
V
VV
V
V
VV
V
A mechanism to rearrange V and C genes in the genome exists so that they can fuse to form a complete
Immunoglobulin gene
CV
C
A single C region gene is encoded in the germline and separated from the multiple V region genes
Find a way to show the existence of multiple V genes and rearrangement to the C gene
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Approach
Tools:
• A set of cDNA probes to specifically distinguish V regions from C regions
• DNA restriction enzymes to fragment DNA
• Examples of germline (e.g. placenta) and mature B cell DNA (e.g. a plasmacytoma/myeloma)
C
VV
VV
V
V
VV
V
Germline DNA
CV
V
VV
V
Rearranged DNA
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* *
*
*
*BB-cell-cellV C
V C
Embryonal cellEmbryonal cell
V-V-CmRNA probeCmRNA probe
CCmRNA probemRNA probe
**
The experiment of Susumi Tonegawa 1976
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The key experiment of Nobumichi Hozumi and Susumu Tonegawa
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There are many vThere are many vaariable genesriable genes but only one constant genebut only one constant gene
V CV V V
GERM LINEGERM LINE
V aV and nd CC g geenes nes gget close to each other in B-ceet close to each other in B-cellls onlyls only
CV V V
BB-CELL-CELL
CONCLUSION
PROTEINPROTEIN
GGENEENE
REARRANGEMENT OF GENE SEGMENTS INTO A SINGLE FUNCTIONAL UNIT (GENE)
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Ig gene sequencing complicated the model
The structures of germline VL genes were similar for V, and V,However there was an anomaly between germline and rearranged DNA:
Where do the extra 13 amino acids come from?
CLVL
~ 95 ~ 100
L CLVL
~ 95 ~ 100
JL
Some of the extra amino acids are provided by
one of a small set of J or JOINING regions
L
CLVL
~ 208
L
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DDuuring ring BB-lymphocyte -lymphocyte developmentdevelopment
Jk Jκ Jκ JκVκ Vκ VκB-cell 1
JκVκB-cell 2
440 V0 Vκκ 55 J Jκκ
Vκ Vκ Vκ Vκ Jκ Jκ Jκ JκGerm lineGerm line
SOMATIC REARRANGEMENT OF KAPPA (κ) CHAIN GENE SEGMENTS
DNA
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pACCκEJJ
Vκ-Jκ
VκVκ P
CCκJVκ ProteinProtein
mRNAmRNACCκJVκ AAAA
TransTranslationlation
EXPRESSION OF THE KAPPA CHAIN
PrimaPrimary ry RNRNAA transcripttranscript
CCκEJJVκLeader
Efficiency of somatic gene rearrangement?
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Further diversity in the Ig heavy chain
VL JL CLL
CHVH JHDHL
The heavy chain was found to have further amino acids (0 – 8) between the JH és CH genes
D (DIVERSITY) region
Each light chain requires 1 recombination eventsVL to JL
Each heavy chain requires 2 recombination events JH to DH , VH to JHDH,
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During B-cell developmentDuring B-cell development
VH2 JH JH
6565 VH VH 66 JH JH
VH1 VH3 D JH JH
2727 D D
D DD
JH JH
JH JHD D
SOMATIC REARRANGMENT OF THE HEAVY CHAIN GENE SEGMENTS
D DVH1 VH2 VH3
VH1 VH2
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HOW MANY IMMUNOGLOBULIN GENE SEGMENTS
Variable (V) 40 30 65
Diversity (D) 0 0 27
Joining (J) 5 4 6
Gene segments Light chain Heavy chain
kappa lambda
Chromosome 2 kappa light chain gene segments
Chromosome 22 lambda light chain gene segments
Chromosome 14 heavy chain gene segments
IMMUNOGLOBULIN CHAINS ARE ENCODED BY MULTIPLE GENE SEGMENTS
ORGANIZATION OF IMMUNOGLOBULIN GENE SEGMENTS
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VHVH DD JHJH
VLVL JLJL
V-DV-Domainsomains
C-DC-Domainsomains
VHVH--DD--JHJH VLVL--JLJL
VARIABILITY OF B-CELL ANTIGEN RECEPTORS AND ANTIBODIES
B cells of one individual 1 2 3 4
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Estimates of combinatorial diversity
Taking account of functional V D and J genes:
65 VH x 27 DH x 6JH = 10,530 combinations
40 Vx 5 J = 200combinations30 Vx 4 J = 120 combinations
= 320 different light chains
If H and L chains pair randomly as H2L2 i.e. 10,530x 320 = 3,369,600 possibilities Due only to COMBINATORIAL diversity
In practice, some H + L combinations do not occur as they are unstableCertain V and J genes are also used more frequently than others.
There are other mechanisms that add diversity at the junctions between genes - JUNCTIONAL diversity
GENERATES A POTENTIAL B-CELL REPERTOIRE
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Somatic recombination to generate antibody diversity
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Severe combined immunodeficiency (SCID)
Early manifestationred rash on the face and shoulders, infections with opportunistic pathogens. (Candida albicans, Pneumocystis carnii pneumonia)Lack of palpable lymph nodes
Omenn syndrome - RAG deficiencyLack of T-cells and B cells
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How does somatic gene rearrangement(recombination) work?
1. How is an infinite diversity of specificity generated from finite amounts of
DNA?
Combinatorial diversity
2. How do V region find J regions and why don’t they join to C regions?
12-23 rule-Special - Recobnitation Signal Sequences (RSS)
- Recognized by Recombination Activation Gene coded proteins (RAGs)
PALINDROMIC SEQUENCES
HEPTAMER CACAGTG CACAGTGGTGACAC GTGACAC
NONAMER ACAAAAACC GGTTTTTGTTGTTTTTGG CCAAAAACA
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V, D, J flanking sequences
V 7 23 9
Sequencing upstream and downstream of V, D and J elements revealed conserved sequences of 7, 23, 9 and 12 nucleotides in an
arrangement that depended upon the locus
V 7 12 9 J7239
J7129
D7129 7 12 9
VH 7 23 9 JH7239
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Recombination signal sequences (RSS)
12-23 RULE – A gene segment flanked by a 23mer RSS can only be linked to a segment flanked by a 12mer RSS
VH 7 23 9
D7129 7 12 9
JH7239
HEPTAMER - Always contiguous with coding sequence
NONAMER - Separated fromthe heptamer by a 12 or 23
nucleotide spacer
VH 7 23 9
D7129 7 12 9
JH7239
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23-mer = two turns 12-mer = one turn
Molecular explanation of the 12-23 rule
Intervening DNAof any length23
V 97
12
D J79
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23-mer
12-mer
Loop of intervening
DNA is excised
• Heptamers and nonamers
align back-to-back
• The shape generated by the
RSS’s acts as a target for
recombinases
7
9
97
V1 V2 V3 V4
V8V7
V6V5
V9 D J
V1 D J
V2
V3
V4
V8
V7
V6
V5
V9
• An appropriate shape can not be formed if two 23-mer flanked elements
attempted to join (i.e. the 12-23 rule)
Molecular explanation of the 12-23 rule
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23-mer
12-mer
V1 D J
V2
V3
V4
V8
V7
V6
V5
V9
7
9
97
CONSEQUENCES OF RECOMBINATIONCONSEQUENCES OF RECOMBINATION
Generation of P-nucleotidesGeneration of P-nucleotides
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23-mer
12-mer
Loop of interveningDNA is excised
V1 D J
V2
V3
V4
V8
V7
V6
V5
V9
7
9
97
Terminal deoxynucleotidyl Transferase (TdT)
Generation of Generation of NN-nucleotides-nucleotides
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V D JTCGACGTTATATAGCTGCAATATA
Junctional Diversity
TTTTTTTTTTTTTTT
Germline-encoded nucleotides
Palindromic (P) nucleotides - not in the germline
Non-template (N) encoded nucleotides - not in the germline
Creates an essentially random sequence between the V region, D region and J region in heavy chains and the V region and J region in light chains
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How does somatic gene rearrangement(recombination) work?
1. How is an infinite diversity of specificity generated from finite amounts of
DNA?
Combinatorial diversity
2. How do V region find J regions and why don’t they join to C regions?
12-23 rule
3. How does the DNA break and rejoin?
Imprecisely, with the random removal and addition of nucleotides to
generate sequence diversity
Junctional diversity (P- and N- nucleotides, see above)