Answer to Question #129833 in Zoology for Junaied Ahmad Wani

Question

An immunology student has isolated protein X, which he believes is a new isotype of human immunoglobulin. Discuss in detail what structural features would protein X have to have in order to be classified as an immunoglobulin?

Answer 1

Structural features that protein X should have to be classified as an immunoglobulin.

Immunoglobulin is a glycoprotein molecule produced by the plasma cells and it functions as an antibody in response to the presence of an antigen. Immunoglobulin is also known as antibodies and they are normally present in serum and tissue fluid. For the isolated protein X to be considered as an immunoglobulin, it should have the following structural features:

·        The protein X should have four linear polypeptide chains arranged in two pairs, heavy and light chains.

·        The light chains are supposed to be lighter and shorter with a molecular weight of about 25kDa. The light chains should contain about 240 amino acids. The difference in amino acid sequence leads to the existence of two types of light chains, the lambda and kappa chains.

·        The heavy chains are supposed to be long and heavy with a molecular weight of about 55-68kDa. The heavy chains contain about 440 amino acids and the two individual chains are connected covalently by disulfide bonds at 1 and 5.

·        Bonding of light and heavy chain should be through single disulfide bond and hydrophobic interactions; the union creates a heterodimer structure that combines with another to create a tetramer structure that appears as “Y” or “I” shape.

·        The heavy chains of an antibody should differ in size, amino acid, and also the carbohydrate content. Based on this, the heavy chain can either contain gamma, epsilon, delta, alpha, or mu chains.

·        An antibody should contain two regions on both light and heavy chain, the variable region for attachment of amino acid, and the constant region for attachment of a carboxy-terminal. The variable regions are responsible for the binding of the antibody to the antigen.