Page 393 - Veterinary Immunology, 10th Edition

VetBooks.ir Immunoglobulin Superfamily

Proteins are constructed by linking multiple peptide domains. Each
domain usually has a specialized function. For example, in proteins

located on cell surfaces, the membrane-binding domain contains
hydrophobic amino acids that can penetrate the cell membrane
lipid bilayer. Other domains may be responsible for the structural
stability of a protein or for its biological activities. In antibody
(immunoglobulin) molecules, one domain is used to bind antigen,

and other domains are responsible for cell binding. The presence of
similar domains in diverse proteins suggests that they have a
common origin, and proteins may be classified into families or

superfamilies based on their domain structure.
Proteins belonging to the immunoglobulin superfamily play key
roles in immunity. The members of this superfamily all contain at
least one immunoglobulin domain. In a typical immunoglobulin
domain the peptide chains weave back and forth to form a pleated

sheet that folds into a sandwich-like structure. Immunoglobulin
domains were first identified in antibody molecules
(immunoglobulins). They have since been found in many other

proteins. Important proteins with multiple immunoglobulin
domains include the B cell antigen receptors (BCRs), the T cell
antigen receptors (TCRs), and the MHC class I and II molecules
(Fig. 14.1). All of the members of this superfamily are receptors,
most are found on cell surfaces, and none has enzymatic activity.

Many cellular responses are triggered by interactions between two
different members of the superfamily as, for example, between TCR
and MHC molecules.

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