Cell Bio Lecture 36 Notes Antibody Structure, Generation of Diversity P. 1216-1227

Myeloma proteins "Bence-Jones proteins" homogeneous antibodies from a single cancerous cell

Bence Jones proteins in urine studied extensively, sequenced, etc. C_LV_L each domain 110aa or so V_L-recognize Ag; C_L-determines kappa or lambda type of light chain.

C_H = 330 or 440 aa, because 3 or 4(IgM, IgE) C_H domains. V_H and V_L determine antibody specificity. Hypervariable and framework regions of V C_H2,3,(4) = F_C

Introns, exons, splicing, 3D structure of domains, intrachain disulfide bonds, hydrophobic binding, etc. support gene duplication model for antibody creation (and Ig superfamily).

Generation of diversity: Germline vs. somatic mutation hypotheses. 10¹⁵ combining surfaces, 10⁵ genes. How can enough diversity be made?10⁵ x 10⁵= 10¹⁰. Also, don't need perfect fit right away.

1976 Susumu Tonegawa: DNA moved during B cell development.

Now, somatic recombination, junctional diversification, somatic hypermutation (much higher rates than normal), random assortment = huge variety of combinations.

[330V X 4J] X [500V X 4J X 12D] X junctional diversification later, affinity maturation.

Make heavy chain V region (try paternal, maternal rearrangements.Try one copy of kappa light, try second copy of kappa light, try first, then second copy of lambda light. If all 4 fail, B cell dies.

Mistakes allowed, still get functional V region, usually...Put onto surface, external signal shuts down rearrangements.

Ag stimulation: make secreted antibody.Class switch as affinity maturation succeeds