Chagasin is a cysteine peptidase inhibitor [1] which forms a beta barrel structure [2].

1: Identification, characterization and localization of chagasin, a tight-binding cysteine protease inhibitor in Trypanosoma cruzi. Monteiro AC, Abrahamson M, Lima AP, Vannier-Santos MA, Scharfstein J; J Cell Sci. 2001;114:3933-3942. PMID:11719560

2: Crystal structure of chagasin, the endogenous cysteine-protease inhibitor from Trypanosoma cruzi. Figueiredo da Silva AA, Carvalho Vieira LD, Krieger MA, Goldenberg S, Tonin Zanchin NI, Guimaraes BG; J Struct Biol. 2006; [Epub ahead of print] PMID:17011790