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BIOL 1104 (30)

Genetic Basis of Antibody Diversity

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BIOL 1104
Tamy Superle

GENETIC BASIS OF ANTIBODY DIVERSITY Structural basis of antigen binding - Antibody sequence variability is clustered variability = # of different observed aa’s/ frequency of most common range = 1(least) – 400(most) observe clustering in 3 HYPERVARIABLE regions interspersed by FRAMEWORK regions true for light and heavy chains **hypervariable regions involved in antigen binding** also called CDR’s (complementarity determining regions) - 3D structure of antibody domains: all domains have IMMUNOGLOBULIN fold all fold independently and there is interaction between HC and LC (VHinteracts w/ V L hypervariable regions cap the distal end - 3D structures of antibody/ligand binding: larger proteins  more interaction (more CDR’s involved) framework residues contact somewhat large interacting surfaces w/ high STERIC complementarity hydrophobics/h-bonds are V. important LITTLE conf. change (saves energy) EPITOPE = minimal amt of antigen needed to bind antibody GENERATION OF IMMUNOLOGIC DIVERSITY due to VDJ recombination somatic hypermutation at least 3 polymorphic alleles of the constant LC region behave as SINGLE GENES same constant region polymorphism (above) linked to several variable regions basis for idea of piecewise recombination of antigen variable region HC and LC are coded PIECEWISE brought together by site specific recombination during B-cell differentiation LC: VJ segment not separated by introns at DNA level preceded and followed by introns that are spliced during txn (1 recombination) HC (more important for variability): VDJ (2 somatic recombinations) 1. DJ joins 2. V joins DJ  VDJ block present as continguous txn unit CDR1,2 located wholly within V (evolutionary) CDR3 located at JUNCTION of VD (built on fly) variable regions for both HC and LC are separated from constant region by intron DETECTION of DNA recombination - restriction digest/southern blotting - PCR MECHANISM OF REARRANGEMENT RSS (recombination signal sequences) flank all unarranged segments conserved 7 and 9 bp separated by 12 OR 23 spacers recognition sites for RECOMBINASE proteins (RAG1/2) check to be
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