module 5: antibodies structure & function

status: unfinished

antibody structure

consists of 4 polypeptides: two identical heavy chains (long) & two identical light chains (short). disulfide (covalent) bonds connect the two heavy chains and the light chains to the heavy chains. each chain has N-terminal domains: V_H (variable domain heavy chain) & V_L (variable domain light chain).

Tiselius & Kabat

showed that gamma fraction of serum contains immunoglobulins that bind antigens. injected rabbits with ovalbumin as an antigen and collected the serum. add ovalbumin into tube B caused it to precipitate (ppt), indicating something in gamma fraction was responsible for binding the antigen. subjected serums into electrophoresis. decreased amount of γ-globulin fraction (tube B): suggested it was responsible for binding Ag, named immunoglobulin/antibody

characterization of gamma globulin protein

gamma globulin (immunoglobulin) was characterized by gel filtration, which separated proteins by molecular weight. MW of IgG = 150,000 daltons.

subunit composition of immunoglobulins

to determine if it was made of subunit polypeptides, it was subjected to mercaptoethanol, which reduced disulfide bonds. after reduction & denaturation, found 2 protein peaks in gel filtration: 50 kd was heavy chain, 25 kd was light chain

papain

pepsin