Three-dimensional structure immunoglobulins

Most of the known antiparallel p structures, including the immunoglobulins and a number of different enzymes, have barrels that comprise at least one Greek key motif. An example is 7 crystallin, which has two consecutive Greek key motifs in each of two barrel domains. These four motifs are homologous in terms of both their three-dimensional structure and amino acid sequence and are thus evolutionarily related. 

All immunoglobulin domains have similar three-dimensional structures... 

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. 

Segal, D.M., et al. The three-dimensional structure of a phosphorylcholine-binding mouse immunoglobulin Fab and the nature of the antigen-binding site. Proc. Natl. Acad. Sci. USA 71 4298-4302, 1974. 

Homologous proteins have similar three-dimensional structures. They contain a core region, a scaffold of secondary structure elements, where the folds of the polypeptide chains are very similar. Loop regions that connect the building blocks of the scaffolds can vary considerably both in length and in structure. From a database of known immunoglobulin structures it has, nevertheless, been possible to predict successfully the conformation of hyper-variable loop regions of antibodies of known amino acid sequence. 

A. Immunoglobulin-like Three-Dimensional Structure of PapD. 104... 

The three-dimensional structure of the PapD periplasmic chaperone that forms transient complexes with pilus subunit proteins has been solved by Holmgren and Branden (1989). PapD consists of two globular domains oriented in the shape of a boomerang (Fig. 2). Each domain is a /3-barrel structure formed by two antiparallel /8-pleated sheets that have a topology similar to an immunoglobulin fold. The relationship between PapD and other immunoglobulin-like proteins is discussed in Section IV,C. 

Figure 33.2. Immunoglobulin G Structure. (A) The three-dimensional structure of an IgG molecule showing the light chains in yellow and the heavy chains in blue. (B) A schematic view of an IgG molecule indicating the positions of the interchain disulfide bonds. N, amino terminus C, carboxyl terminus.

Richardson, J. S., Richardson, D. C., Thomas, K. A., Silverton, E. W., and Davies, D. R. Similarity of three-dimensional structure between the immunoglobulin domain and the copper, zinc superoxide dismutase subunit. J. Molec. Biol. 102, 221-235 (1976). 

Most of the components that conuihute to cellular homeostasis are proteins—so much so that more than half of the dry weight of a cell is protein. Histones, cellular enzymes, membrane transport systems, and immunoglobulins are just a few examples of the proteins that carry out the biological functions of a living human cell. Proteins are hydrated three-dimensional structures, but at their most basic level, they are composed of linear sequences of amino acids that fold to create the spatial characteristics of the protein. These linear... 

It is doubtful whether studies on antibodies would have advanced as rapidly had not a substantial body of data on the specificity, sequence, and three-dimensional structure been accumulated on the immunoglobulins and related molecules associated with certain neoplastic diseases. A large proportion of patients with a disease of plasma cells called multiple myeloma had been known for over a century to excrete in their urine large amounts of a class of protein named... 

How do these fragments relate to the three-dimensional structure of whole IgG molecules Immunoglobulin G consists of two kinds of polypeptide chains, a 25-kd light (L) chain and a 50-kd heavy (H) chain (Figure 33.5), The subunit composition is L2H2. Each L chain is linked to an H chain by a disulfide bond, and the H chains are linked to each other by at least one disulfide bond. Examination of the amino acid sequences and three-dimensional structures of IgG molecules reveals that each L chain comprises two homologous domains, termed immunoglobulin domains, to be... 

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