A dodecameric protease complex with a tetrahedral shape (TET) was isolated from Haloarcula marismortui, a salt-loving archaeon. The 42 kDa monomers in the complex are homologous to metal-binding, bacterial aminopeptidases. TET has a broad aminopeptidase activity and can process peptides of up to 30-35 amino acids in length. TET has a central cavity that is accessible through four narrow channels (<17 A wide) and through four wider channels (21 A wide). This architecture is different from that of all the proteolytic complexes described to date that are made up by rings or barrels with a single central channel and only two openings.