Antibody structure

\( \newcommand\) • • • • • • • Skills to Develop • Explain cross-reactivity • Describe the structure and function of antibodies • Discuss antibody production An antibody, also known as an immunoglobulin (Ig), is a protein that is produced by plasma cells after stimulation by an antigen. Antibodies are the functional basis of humoral immunity. Antibodies occur in the blood, in gastric and mucus secretions, and in breast milk. Antibodies in these bodily fluids can bind pathogens and mark them for destruction by phagocytes before they can infect cells. Antibody Structure An antibody molecule is comprised of four polypeptides: two identical heavy chains (large peptide units) that are partially bound to each other in a “Y” formation, which are flanked by two identical light chains (small peptide units), as illustrated in Figure \(\PageIndex\): (a) As a germ-line B cell matures, an enzyme called DNA recombinase randomly excises V and J segments from the light chain gene. Splicing at the mRNA level results in further gene rearrangement. As a result, (b) each antibody has a unique variable region capable of binding a different antigen. Similar to TCRs and BCRs, antibody diversity is produced by the mutation and recombination of approximately 300 different gene segments encoding the light and heavy chain variable domains in precursor cells that are destined to become B cells. The variable domains from the heavy and light chains interact to form the binding site through which an ant...

\( \newcommand\) • • • • • • An antibody is a Y-shaped protein produced by B cells to identify and neutralize antigens in the body. Key Points • An antibody, also known as an immunoglobulin, is a large Y-shaped protein produced by B- cells and used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. • Each tip of the “Y” of an antibody contains a paratope (a structure analogous to a lock) that is specific for one particular epitope (similarly analogous to a key) on an antigen, allowing these two structures to bind together with precision. • Though the general structure of antibodies is very similar, a small region at the tip of the protein is extremely variable, allowing millions of antibodies with different antigen binding sites to exist. This region is known as the hypervariable region. • Five isotypes of antibodies are found in different locations and perform different specific functions. • The base of the Y plays a role in modulating immune cell activity. This region is called the Fc region, and phagocytes may bind to it to initiate phagocytosis. • Antibodies that bind to surface antigens on a bacterium attract the first component of the complement cascade with their Fc region and initiate activation of the classical complement system. Key Terms • epitope: Part of a biomolecule (such as a protein) that is the target of an immune response. • paratope: Part of the molecule of an antibody that binds to an antigen. • isotype: A mar...

Immunoglobulins, also known as antibodies, are glycoprotein molecules produced by plasma cells or white blood cells. They specifically recognize and bind to particular antigens. This page introduces the nomenclature and criteria used to describe the structure, classes, and functional types of immunoglobulins. Explore antibodies Introduction to immunoglobulins Heavy and light chains are held together by a combination of non-covalent interactions and covalent interchain disulfide bonds, forming a bilaterally symmetric structure. The V regions of H and L chains comprise the antigen-binding sites of the immunoglobulin (Ig) molecules. Each Ig monomer contains two antigen-binding sites and is said to be bivalent. The hinge region is the area of the H chains between the first and second C region domains and is held together by disulfide bonds. This flexible hinge (found in IgG, IgA, and IgD, but not IgM or IgE) region allows the distance between the two antigen-binding sites to vary. The five primary classes of immunoglobulins are IgG, IgM, IgA, IgD, and IgE. These are distinguished by the type of heavy chain found in the molecule. IgG molecules have heavy chains known as gamma-chains; IgMs have mu-chains; IgAs have alpha-chains; IgEs have epsilon-chains; and IgDs have delta-chains. Differences in heavy chain polypeptides allow these immunoglobulins to function in different types of immune responses and at particular stages of the immune response. The polypeptide protein sequence...

Antibodies, like other proteins, can be covalently modified in many ways to suit the purpose of a particular assay. Many immunological methods involve the use of labeled antibodies and a variety of reagents have been created to allow labeling of antibodies. Enzymes, biotin, fluorophores and radioactive isotopes are all commonly used to provide a detection signal in biological assays. Explore antibody labeling kits Overview of Protein Labeling Understanding the functional groups available on an antibody is the key to choosing the best method for modification, whether that be for • Primary amines (–NH2):these occur on lysine residues and the N-terminus of each polypeptide chain. They are numerous and distributed over the entire antibody. • Sulfhydryl groups (–SH):these occur on cysteine residues and exist as disulfide bonds that stabilize the whole-molecule structure. Hinge-region disulfides can be selectively reduced to make free sulfhydryls available for targeted labeling. • Carbohydrates (sugars):glycosylation occurs primarily in the Fc region of antibodies (IgG). Component sugars in these polysaccharide moieties that contain cis-diols can be oxidized to create active aldehydes (–CHO) for coupling. The most common target for antibody labeling or conjugation is primary amines, which are found primarily on lysine residues. They are abundant, widely distributed and easily modified because of their reactivity and their location on the surface of the antibody. Primary amines c...