Disulphide bonds immunoglobulin

IgG consists of four polypeptide subunits held together by disulphide bonds. Native immunoglobulins are rather resistant to proteolytic digestion but certain enzymes have been usefiil in elucidating their structure. Papain cleaves the molecule into three fragments of similar size ... 

Figure 1.13. Schematic representation of an IgA molecule. Each IgA molecule comprises immunoglobulin molecules joined to each other via a J chain. The heavy chains possess three constant regions (Co1 Cce). The secretory chain (SC) is secreted by epithelial cells and binds to the IgA dimer via disulphide bonds (indicated by wriggly lines).

Fig. 2. Presently known members of the immunoglobulin superfamily. 0. immunoglobulin-like V units O- units distantly related to immunoglobulin V units non-immunoglobulin-like V units O- C units Interchain disulphide bonds are not shown. The double line represents the plasma membrane to which Thy-1 and a form of NCAM are attached via a link to a phophoinositide. The structure of the TcR 5 chain is hypothetical.

Figure 4.28 Model of the basic 7S immunoglobulin (Ig) molecule showing two heavy and two light chains joined by disulphide bonds V, variable region C, constant region L, light chain H, heavy chain 1, 2 and 3 subscripts refer to the three constant regions of the heavy chains CHO, carbohydrate groups Fab refers to the (top) antigen-specific portion of the Ig molecule Fc refers to the cell-binding effector portion of the Ig molecule (from Larson, 1992).

Sheep erythrocytes sensitized with intact immunoglobulin G or with reduced (dithioerythritol) and alkylated (iodoacetamide) antibody have been lysed by guinea-pig serum, indicating that reduced and alkylated antibody bound and activated complement. Observations suggested that the sole effect of reduction of antibody disulphide bonds was to diminish the co-operativity of antibody-complement interaction. 

Figure 1.6 Sequences around the disulphide bridges in the ChI region of human immunoglobulins of different subclasses. Note that yl is the only H chain subclass that does not have the H—L disulphide bond at position 131. Established points of differences between yl, 2,3, and 4 are underlined.

Each immunoglobulin molecule (Figure 4.18) consists of two identical light chains (kappa or lambda) which are attached to two identical heavy chains by covalent bonds. The two heavy chains are also interlinked by disulphide bonds. 

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