Antibody structure and function: http://www.creative-diagnostics.com/Antibody-Structure-and-Function.htm\n\n
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A typical antibody molecule (IgG, centre) has 12 domains, arranged in two heavy and
two light (H and L) chains, linked through cysteine residues by disulphide bonds so
that the domains lie together in pairs, the whole molecule having the shape of a
flexible Y. In each chain the N-terminal domain is the most variable, the rest being
relatively constant. Within the variable (V) regions, the maximum variation in amino
acid sequence is seen in the six hypervariable regions (three per chain) which come
together to form the antigen-binding site (bottom left in figure).
The constant (C) regions vary mainly in those portions that interact with complement
or various cell-surface receptors; the righthand part of the figure 1 shows the
different features of the C region in the five classes of antibody: M, G, A, E and D. The
result is a huge variety of molecules able to bring any antigen into contact with any
one of several effective disposal mechanisms. The basic structure (MW about 160
000) can form dimers (IgA, MW 400 000) or pentamers (IgM, MW 900 000).
There are species differences, especially in the heavy chain subclasses, which have
evolved comparatively recently; the examples shown here illustrate human
antibodies. Interestingly, camels and llamas also have antibodies with only heavy
chains. These antibodies may be able to attach to some targets not accessible to
conventional antibodies, and examples are being tested as possible new ways of
preventing infection by viruses such as HIV. Find more about antibody structure and
function at Creative Diagnostics.