Protein A ( Eng. Protein A ) - a protein with a molecular weight of 40 - 60 k Yes , isolated from the surface of the cell wall of Staphylococcus aureus ( Staphylococcus aureus ). Protein A is used in biochemical studies, as it binds well many mammalian immunoglobulins , especially class G immunoglobulins .
Protein A binds to the F c region of antibodies, while interacting with heavy chains . The role of protein A in the pathogenesis of staphylococcal infection is that IgG molecules bind to the surface of bacterial cells in the wrong orientation. This leads to impaired opsonization and phagocytosis .
Protein A is encoded by the spa gene , and its regulation is controlled by DNA topology, osmolarity in the cell, and the two-component ArlS – ArlR system.
Content
Specificity
Protein A binds with high affinity human IgG1, IgG2 and IgG4, as well as mouse IgG2a, IgG2b and IgG3; with moderate affinity - human IgM, IgA and IgE, as well as mouse IgG3 and IgG1 [1] . Protein A does not bind human IgG3, IgD, Fab, scFv, and does not bind mouse IgM, IgA or IgE.
Other immunoglobulin binding proteins
There are also other bacterial proteins that bind immunoglobulins - protein G , protein A / G and protein L. These bacterial proteins are used for purification, immobilization and detection of immunoglobulins. These proteins have different affinities for different classes and subclasses of immunoglobulins.
Importance in Pathogenesis
Staphylococcus aureus uses protein A, along with other surface proteins, to survive in the host and ensure virulence. Mutant bacteria S. aureus , which do not have protein A on the surface, are more efficiently phagocytosed in vitro and have reduced virulence .
Research
Recombinant staphylococcus A protein is often obtained in E. coli and is used for research in biology and immunology. One of the recombinant forms of protein A is called MabSelect and is used to isolate monoclonal antibodies .
Protein A is often combined with other molecules, for example, fluorescent dyes, enzymes , biotin , colloidal gold or radioactive iodine . In this case, the binding site of the antibody does not change.
See also
- Protein G
Literature
- Fournier, B and Klier A. 2004. Protein A gene expression is regulated by DNA supercoiling which is modified by the ArlS-ArlR two-component system of Staphylococcus aureus . Microbiology 150, 3807-3819.