B. anthracis PA83

PA acts as the "gateway" that allows the translocation and action of both toxins. Full-length PA is an 83-kDa polypeptide (PA83) that is rapidly cleaved by cell surface proteases such as furin to a 63-kDa form (PA63). Only the PA63 form oligomerizes as heptamers or octamers that provide the binding sites for LF or EF. The oligomer bound to one or more molecules of LF/EF is then rapidly translocated into cells.