Plastic Surgery Clinics Sloane Square

BoNT-A is a neurotoxin secreted by Clostridium Botuli and purified to be used in therapeutics. There is seven serotypes ( A,B,C,D,E,F,G) but only BoNT-A and BoNT-B are licensed for focal dystonia treatment. BoNT-A is a polypeptide with 2 chains linked by a disulfuric bridge. The heavy chain is responsible of the specific binding of the BoNT-A to the cholinergic fibers. The limited action on cholinergic fibers due to this specific bindings is one factor of safety of the BoNT-A . The light chain is responsible of the enzymatic action of the BoNT-A, which cuts a membrane vesicle protein ( called SNAP-25), making the release of the acetylcholine in the synaptic cleft impossible. When the release of the acetylcholine is blocked, there is no more signal from the nerve to the muscle , therefore the muscle is less able to contract. Also there is no more signal between the nerve and the glands ( sweat or salivary glands for example), and the gland stops secreting. This blockage of the release of the acetylcholine is transient, as there is sprouting of the nerve terminals and also synthesis of new membrane vesicle proteins.