Protein A
| Immunoglobulin G binding protein A ( Staphylococcus aureus ) | ||
|---|---|---|
| Mass / length primary structure | 441 amino acids | |
| Identifier | ||
| Gene name (s) | spa | |
| External IDs | ||
Protein A is a protein of 40 to 60 kDa in size that originally comes from the cell wall of the bacterium Staphylococcus aureus . It is widely used in biochemical research because of its ability to bind immunoglobulins . Proteins from various mammalian species are bound, especially IgG.
Protein A binds to the Fc region of the immunoglobulins by interacting with the heavy chain. The bacterium protects itself in the body against the defense mechanisms of the immune system; as the antibodies bind to the cell wall "the wrong way round" (compared to their normal function), it is protected from opsonization and phagocytosis .
Antibody binding by protein A
Protein A binds with high affinity to human IgG1 and IgG2 as well as to IgG2a, IgG2b and IgG3 of the mouse. Human IgM, IgA and IgE as well as mouse IgG1 are bound with moderate affinity. In contrast, it reacts neither with human IgG3 or IgD nor with IgM, IgA or IgE of the mouse.
Role in pathogenesis
Staphylococcus aureus uses protein A as a pathogen , along with a number of other proteins and surface factors to ensure its survival. By binding the host's own antibodies, protein A prevents recognition by the host's immune system and phagocytosis by phagocytotic cells such as macrophages . Mutants of S. aureus that cannot express protein A are phagocytosed more quickly in vitro and show lower virulence in infection models .
A current study shows that protein A also kills B lymphocytes very efficiently, which play an important role in the immune defense against bacterial infections. This could be of pharmaceutical benefit because B-lymphocytes also play a crucial role in some autoimmune diseases such as rheumatoid arthritis and lupus erythematosus ; the suppression of the B-cell response could lead to new therapies for autoimmune diseases.
application
Protein A, like Protein G or Protein A / G , is used in biochemistry for protein purification and the measurement of antibodies. Recombinant staphylococcal protein A is mostly produced in E. coli for use in immunological and biological research. Often the protein is labeled with other substances, such as fluorescent dyes , enzymes , biotin , colloidal gold or radioactive iodine ( 125 I). Protein A is often coupled to microparticles ( beads ), be it magnetic beads, latex or sepharose . Protein A is well suited for the purification of IgG from protein mixtures such as B. serum, or, coupled to one of the markers mentioned above, for the detection of antibodies. Coupled to Sepharose , protein A is used in immunoprecipitation .
credentials
- ↑ CS Goodyear, GJ Silverman: Death by a B-cell superantigen: In vivo VH-targeted apoptotic supraclonal B-cell deletion by a staphylococcal toxin. In: J. Exp. Med. Volume 197, 2003, pp. 1125-1139. PMID 12719481