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Antibodies Are Heterodimers,Immune system,Immunity.

Posted by Mumtaz khan Friday, 17 February 2012

Basic structure of antibodies: Antibodies are Heterodimers                Antibody molecules have a common structure of four peptide chains.This structure of two identical light(L)chains, polypeptides of about 25,000 molecular weight,and two identical heavy(H)chains,larger polypeptides of molecular weight 50,000 or more.Like the antibody molecules they constitute,h and L chains are also called immunoglobulins.Each light chain is bound to a heavy chain by a disulfide bond,and by such noncovalent interactions as salt linkages,hydrogen bonds,and hydrophobic bonds,to form a heterodimer(H-L)chain combinations to each other to form the basic four-chain(H-L)(H-L)antibody structure,a dimer of dimers.As we shall see,the exact number and precise positions of these interchain disulfide
 bonds differs among antibody classes and subclasses.

     The first 110 or so amino acids of the amino-terminal region of a light or heavy chain varies greatly among antibodies of different specificity.These segments of highly variable sequence are called V regions.All the differences in specificity displayed by different antibodies can be traced to differences in the amino acid sequences of V regions.In fact,most of the differences among antibodies fall within areas of the V regions called complementary-determining regions(CDRs),and it is these CDRs on both light and heavy chains,that constitute the antigen-binding site of the antibody molecule.By contrast,within the same antibody class,far fewer differences are seen when one compares sequences throughout the rest of the molecule.The regions of relatively constant sequence beyond the variable regions have been dubbed C regions.Antibodies are glycoproteins;with few exceptions,the sites of attachment for carbohydrates are restricted to the constant region.We do not completely understand the role played by glycosylation of antibodies,but it is probably increases the solubility of the molecules.Inappropriate glycosylation,or its absence,affects the rate at which antibodies are cleared from the serum,and decreases the efficiency of distraction between antibody and the complement system and between antibodies and Fc receptors.


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