Heavy chains, IgG

Anti-DNA immunoglobulin heavy chain IgG [Mus musculus] GI 1872464 Anti-DNA immunoglobulin light chain IgG [Mus musculus] GI 1870507... 

In nature, mammalian antibodies occur in five distinct classes IgG, IgA, IgM, IgD, and IgE. These differ in structure, size, amino acid composition, charge, and carbohydrate components. The basic structure of each of the classes of immunoglobulins consists of two identical polypeptide chains linked by disulfide bonds to two identical heavy chains. Differences between classes and subclasses are determined by the makeup of the respective heavy chains. IgG is the major serum immunoglobulin and occurs as a single molecule IgA also occurs as a single molecule but also polymerizes, primarily as a dimer and also associates with a separate protein when secreted. IgM occurs in the serum as a pentamer, with monomers linked by disulfide bonds and the inclusion of an additional polypeptide component, the J-chain. IgD and IgE occur primarily as membrane-bound monomers on -cells, or basophils and mast cells, respectively. 

These deseriptions deal with the processing of the donor serum after production and before conjugation. The description of the immimogen is also sometimes critical. Using the last example, the cow IgG may have itself been affinity purified before injection of the donkey, or specific parts of the Ig purified to raise a subclass specific antiserum, for example, heavy chain IgG may have been... 

Serum contains antibodies of the classes IgG, IgM, IgA, IgE, and IgD. The classes differ in their heavy chains. The IgG antibodies have the highest concentration in the serum (8 to 16 mg/ml). They are synthesized by B lymphocytes and have two heavy chains of the y tjrpe (Figure 6.1). The subclasses of the IgG antibodies (IgGi, IgG2a, IgG2b, IgGs, and so on) differ in the C-terminal end of the heavy chains. IgG antibodies are stable proteins. They withstand low concentrations of SDS (0.05%) and several freeze/thaw cycles. 

Fig. 4. Simple model of an IgG molecule showing light- and heavy-chain segments where a line ( ) between the chains represents a disulfide bond. General Methodology.

The basic structure of all immunoglobulin (Ig) molecules comprises two identical light chains and two identical heavy chains linked together by disulfide bonds (Figure IS.2a). There are two different classes, or isotypes, of light chains, X and k, but there is no known functional distinction between them. Heavy chains, by contrast, have five different isotypes that divide the immunoglobulins into different functional classes IgG, IgM, IgA, IgD, and IgE, each with different effector properties in the elimination of antigen... 

In this chapter we will discuss immunoglobulins of the IgG class, which is the major type of immunoglobulin in normal human serum, and which has the simplest structure. Each chain of an IgG molecule is divided into domains of about 110 amino acid residues. The light chains have two such domains, and the heavy chains have four. 

The most remarkable feature of the antibody molecule is revealed by comparing the amino acid sequences from many different immunoglobulin IgG molecules. This comparison shows that between different IgGs the amino-terminal domain of each polypeptide chain is highly variable, whereas the remaining domains have constant sequences. A light chain is thus built up from one amino-terminal variable domain (Vl) and one carboxy-terminal constant domain (Cl), and a heavy chain from one amino-terminal variable domain (Vh), followed by three constant domains (Chi, Ch2. and Chs). 

IgG antibody molecules are composed of two light chains and two heavy chains joined together by disulfide bonds. Each light chain has one variable domain and one constant domain, while each heavy chain has one variable and three constant domains. All of the domains have a similar three-dimensional structure known as the immunoglobulin fold. The Fc stem of the molecule is formed by constant domains from each of the heavy chains, while two Fab arms are formed by constant and variable domains from both heavy and light chains. The hinge region between the stem and the arms is flexible and allows the arms to move relative to each other and to the stem. 

In a comparative study of disulfide reducing agents, it was determined that use of the relatively strong reductants DTT and TCEP required only 3.25 and 2.75 mole equivalents per mole equivalent of antibody molecule to achieve the reduction of two interchain disulfide bonds between the heavy chains of a monoclonal IgG (Sun et al., 2005). This limited reduction strategy retains intact bispecific antibody molecules while providing discrete sites for conjugation to thiols. 

Figure 20.10 Digestion of IgG class antibodies with pepsin results in heavy chain cleavage below the disulfide groups in the hinge region. The bivalent fragments that are formed are called F(ab )2. The remaining Fc region normally is severely degraded into smaller peptide fragments.

Figure 20.12 F(ab )2 fragments produced by pepsin digestion of IgG can be reduced at their heavy chain...

Antibody, scFv, against carcinoembryonic antigen Callus Oryza sativa (rice) Microparticle bombardment of callus Maize ubiquitin-1 Murine heavy-and light-chain IgG 0.45 jig g"1 fresh weight without KDEL (i) 3.8 jug g-1 fresh weight with KDEL (i) 31... 

Fig. 15.1 Antibodies and antibody fragments produced in plant systems. A- In the conventional IgG, the constant heavy-chain CHI,...

The classical Y shape of the IgG molecule (MW 150 kD) is composed of four polypeptide chains two identical light chains (each has a molecular weight of 25 kD), and two identical heavy chains (each has a molecular weight of 50 kD)... 

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