Cyclic heptapeptide that belongs to the MSDIN-like toxin family responsible for a large number of food poisoning cases and deaths (PubMed:27978833). Cycloaminide B is non-toxic to mammals but shows immunosuppressive activity, probably through the inhibition of the action of interleukin-1 and interleukin-2 (PubMed:27978833, PubMed:8441706). Processed by the macrocyclase-peptidase enzyme POPB to yield a cyclic decapeptide (By similarity). POPB first removes 10 residues from the N-terminus (PubMed:28866879). Conformational trapping of the remaining peptide forces the enzyme to release this intermediate rather than proceed to macrocyclization (By similarity). The enzyme rebinds the remaining peptide in a different conformation and catalyzes macrocyclization of the N-terminal 7 residues (PubMed:28866879). Belongs to the MSDIN fungal toxin family.