Not everybody working in immunobiology has an in-depth knowledge of the subject. Some may be students, who are still getting to grips with the discipline at college. Others may have been forced into a swift career change following restructuring at work. For whatever reason, people quite often perform their first antibody assays with only the vaguest knowledge of the underlying concepts. Understanding the molecular structure of a given antibody is fundamental to interpreting its results, therefore we at Novus Biologicals have put a few basic facts together.
Antibodies are glycoproteins composed of one or more Y-shaped polypeptide units. Each of these has two identical heavy (H) and two light (L) chains, forming the left and right binding sites of the Y. The H chains are hinged, and have roughly double the number of amino acids (and therefore molecular weight) of the light chains. The L-chains are non-hinged, and sit inside the ‘arms’ of the Y.
The regions of polypeptide chains are called domains. The amino terminal end of each chain is termed the variable (V) domain. V-domains show considerable diversity compared to the C (constant) domains, and are where antigen binding takes place.
L-chains contain one variable domain VL, and one constant domain CL. The H-chains have one variable domain VH, plus 3 constant domains CH1, 2 and 3. The CH1 and CH2 domains sit either side of the hinge. Each H-L pair forms a single binding site, meaning each antibody unit is a bivalent monomer.
There are five primary antibody classes, and a number of sub-classes. Variations in the heavy-chain polypeptides and number of monomers allow them individual functions in the immune response.
