Pertussis toxin is a large protein produced by Bordatella pertussis, causing whooping cough. It disrupts intracellular signaling mechanisms, facilitating bacterial colonization. The A/B toxin has six subunits, with S1 having enzymatic activity and S2-S5 binding to receptors on the host cell membrane. The toxin impairs intracellular signaling by adding ADP-ribose to G protein, interfering with the immune response. The toxin’s subunits S2 and S3 bind to different cell types, and the toxin is used in biochemical research on G proteins.
Pertussis toxin is a large protein produced by Bordatella pertussis, the causative agent of whooping cough. Also known as PT, the toxin is a large protein made up of six subunits. It is an exotoxin and is released from bacterial cells in an inactive form. Once absorbed into cells, it is activated, disrupting the intracellular signaling mechanisms of its host cells and facilitating bacterial colonization of the infected person. This bacterial disease is one of the contagious diseases that affects both children and adults despite the existence of a vaccine against the organism.
There are six subunits of pertussis toxin, known as S1, S2, S3, S4 and S5. There are two S4 subunit molecules in each PT molecule. This type of toxin is known as an A/B toxin. Part A of pertussis toxin is composed of S1, has enzymatic activity and can catalyze chemical reactions.
Section B of PT contains the S2-S5 subunits and bind to receptors on the host cell membrane. Once an appropriate compound binds to it, this triggers cellular activity. The binding of the B parts of the pertussis toxin causes the activation of the A subunit. Once this subunit is active, it interferes with the host’s immune response.
An important part of the human immune system is the activation of receptors called G proteins. They stimulate many pathways involved in immunity. If their activity is blocked, this can greatly interfere with the ability to fend off a pathogenic attack. Activation of the A-subunit of pertussis toxin adds ADP-ribose to a form of G protein, thereby greatly impairing intracellular signaling and interfering with an immune response to infection with this Bordatella pathogen.
The pertussis toxin subunits S2 and S3 bind to receptors on different cell types. Subunit 3 can bind to the surface of cells called phagocytes, whose function is to absorb and absorb bacteria and other invaders. It is unclear why the pathogen triggers this response. One hypothesis is that by being inside these specialized cells, pathogenic bacteria are able to limit another aspect of the immune system. Normally these cells would produce toxic oxidized products that would kill nearby bacteria.
Biochemical research on G proteins often uses the commercially available pertussis toxin. The ability of this subunit to add ADP-ribose to G protein causes its activity to be separate from any G protein receptor responses. This is useful for G protein studies. It comes in an inactive form and does not require activation when used with cell extracts or cells, but it does when experiments involving purified G protein.
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