similar to SP:P13423; identified by sequence similarity; putative
Protein Annotation
Protective antigen (PA) is the dominant antigen in both natural and vaccine-induced immunity to anthrax infection and consists of four distinct and functionally independent domains. Domain 1 is divided into domains 1a (consisting of amino acids 1-167) and 1b (consisting of aa 168-258). Domain 2 comprises aa 259-487 and domain 3 aa 488-595. After the antigen binds to the host cell receptor via the binding site of domain 4, the N-terminal amino acids (1-167, i.e. domain 1a) of domain 1, which contain a furin protease cleavage site, are cleaved off, exposing the LF or EF binding site located in domain 1b and the adjacent domain 3. Domains 2 and 3 then form part of a heptameric pore on the cell surface, the LF or EF binds to its receptor, and the whole toxin complex undergoes receptor-mediated endocytosis into the cell. After acidification of the endosome, the toxin is translocated into the cell cytosol where it exerts its cytotoxic effect. Therefore, inhibition of the binding and entry of the toxin complex, particularly lethal toxin, into the host cell is clearly important for the prevention of infection (Flick-Smith et al., 2002).