Sandbox 300: Difference between revisions

''Staphylococcus aureus'' is known to be a dangerous pathogen, which is responsible for food poisoning and localized or generalized infections. This bacterium is often associated to multi-resistant germ to antibiotics, and it causes problems in medical field.

The pathogenicity of ''S. aureus'' is due to protein A, which is one of various other important virulence factors.

The protein A permits the inhibition of the phagocytosis, the process of vesicular internalization of solid particles, thanks to the interaction with mammal antibodies.  

In a normal case of phagocytosis the bacteria are eliminated during intracellular digestion, thanks to hydrolytic enzymes of phagocytes. At first, the particle is recognized and sticks to the phagocyte. The recognition is possible thanks to phagocyte membrane receptors, which recognize the Fc domain of immunoglobulins. Then the bacteria enter into the phagocyte by a process of endocytosis. The intracellular digestion takes place, and the bacteria are degraded by enzymes. Finally, cell fragments are removed by exocytosis.  

If ''S.aureus'' is located in the serum, the interaction between the Fc domain and protein A leads to the attachment in a wrong direction of the IgG to the bacteria: then, the recognition is not allowed and the cascade of reactions necessary for phagocytosis does not occur. By stopping this process and through other virulence factors, bacterial colonization is allowed through the growth and dissemination of bacteria into the organism<ref>http://en.wikipedia.org/wiki/Protein_A?oldid=252478781</ref>.  

Thanks to its properties against immunoglobulins, protein A is used in research in technics of purification of antibodies; this kind of purification is called “Class-specific Affinity”.

To accomplish the purification of IgG, the IgG-binding protein is immobilized onto a solid supports, like porous resins (for example, beaded agarose) or magnetic beads. This protein is often used, because it has an advantage: there are no orientation problems thanks to the 5 binding domains of protein A with IgG. But this protein is relatively specific to IgG; for example, it binds very poorly or not to all IgM. In order to bind other antibody targets, the use of other proteins is required, such as protein L or G, which have different binding properties.