IgG molecule

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.

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). 

Huber, R., et al. Crystallographic structure studies of an IgG molecule and an Fc fragment. Nature 264 ... 

Receptors for Fc fragments of IgGs 1 Bind Fc fragments of IgG molecules Target antigen-antibody complexes to myeloid and lymphoid cells, eliciting phagocytosis and other responses... 

Figure 1.77 Disulfide reducing agents such as 2-mercaptoethylamine can be used to cleave the disulfide bonds in the hinge region of antibody molecules. Either intact IgG molecules or F(ab )2 fragments may be reduced in this manner to yield monofunctional antigen binding fragments.

Add TCEP to a final concentration of 20 mM. For partial reduction of antibody disulfides in the hinge region while maintaining a biospecific IgG molecule, add TCEP in a 2.75-fold molar excess over that of the antibody concentration. 

Similarly, the two light chains of an antibody are identical and have a molecular weight of about 25,000. For IgG molecules, the intact molecular weight representing all four subunits is in the range of 150,000-160,000. 

Figure 20.4 Reduction of the disulfide bonds within the hinge region of an IgG molecule produces half-anti-body molecules containing thiol groups. Reaction of these reduced antibodies with a maleimide-activated enzyme creates a conjugate through thioether bond formation.

Fig. 15.4 Structure of glycans N-linked to IgG molecules expressed in hybridomas and transgenic plants. Glycans N-linked to plant-derived antibodies are structurally different from their mammalian counterparts. In contrast with antibodies produced in alfalfa, antibodies produced in tobacco plants present a very high glycan heterogeneity.

Ovary, Z., Passive cutaneous anaphylactic reactions as tools in the study of the structure of the IgG molecule, Mol. Immunol., 15, 751, 1978. 

Figure 8. Surface pressure - area isotherms for stearylamine before (a) and after (b) adsorption of IgG at pH 8, 20 °C, and schematic representation for IgG molecule adsorbed to stearylamine monolayer.

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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