3.2 Structural domains
Structural domains can serve as spacers, which position other domains in an appropriate orientation or location, or they may permit movement of domains relative to each other. Examples of domains that function as spacers are the heavy and light immunoglobulin constant domains which ‘present’ the working end of the immunoglobulin, i.e. the variable domains, for binding to target antigen (Figure 27).
Figure 27 Immunoglobulin domains. The heavy and light chains of the immunoglobulin molecule both contain variable (VH and VL) and constant (CH and CL) domains. The variable domains make up the antigen binding site.