The staphostatin A polypeptide chain folds into a slightly deformed, eight-stranded beta-barrel, with strands beta-4 through beta-8 forming an antiparallel sheet while the N-terminus forms a a psi-loop motif. Members of this family constitute a class of cysteine protease inhibitors distinct in the fold and the mechanism of action from any known inhibitors of these enzymes [1].

1: A novel class of cysteine protease inhibitors: solution structure of staphostatin A from Staphylococcus aureus. Dubin G, Krajewski M, Popowicz G, Stec-Niemczyk J, Bochtler M, Potempa J, Dubin A, Holak TA; Biochemistry. 2003;42:13449-13456. PMID:14621990