Cyclic decapeptide that belongs to the MSDIN-like toxin family responsible for a large number of food poisoning cases and deaths (PubMed:4966639). Counteracts the lethal action of the Amanita toxins phalloidin and alpha-amanatin if administered before, or simultaneously with, the poisons (PubMed:4966639, PubMed:2442001). Acts probably through competitive antagonism (PubMed:2442001). Its concentration in the fungus is, however, so low that the toxic action of the latter predominates (PubMed:4966639). Shows immunosuppressive activity, probably through the inhibition of the action of interleukin-1 and interleukin-2 (PubMed:2033005, PubMed:1494502). Antamanide inhibits the mitochondrial permeability transition pore, a central effector of cell death induction, by targeting the pore regulator cyclophilin D (PubMed:21297983). Processed by the macrocyclase-peptidase enzyme POPB to yield a cyclic decapeptide (PubMed:28866879). POPB first removes 10 residues from the N-terminus (By similarity). 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 10 residues (PubMed:28866879). Antamanide reduces multiorgan injury induced by IL-2, such as lung, hart and kidney edema; but does not have the toxicity of related cyclopeptides such as phalloidin (PubMed:2033005). Belongs to the MSDIN fungal toxin family. The linear sequence initially published does not reflect the actual order of residues as encoded by the genome which begins with a Phe residue and ends with a Pro residue, the latter being important for cyclization (PubMed:4966639).