Dissimilar Reactions and Enzymes for Psilocybin Biosynthesis in Inocybe and Psilocybe Mushrooms

Psilocybin (4-phosphoryloxy-N,N-dimethyltryptamine, 1) is the main indolethyl-amine natural product of psychotropic (so-called "magic") mushrooms. The majority of 1-producing species belongs to the eponymous genus Psilocybe, for which the biosynthetic events, beginning from l-tryptophan (2), and the involved enzymes have thoroughly been characterized. Some Inocybe (fiber cap) species, among them Inocybe corydalina, produce 1 as well. In product formation assays, we characterized four recombinantly produced biosynthesis enzymes of this species in vitro: IpsD, a pyridoxal-5'-phosphate-dependent l-tryptophan decarboxylase, the kinase IpsK, and two near-identical methyltransferases, IpsM1 and IpsM2. The fifth enzyme, the insoluble monooxygenase IpsH, was analyzed in silico. Surprisingly, none of the reactions intrinsic to the 1 pathway in Psilocybe species takes place in I. corydalina. Contrasting the situation in Psilocybe, the Inocybe pathway is branched and leads to baeocystin (4-phosphoryloxy-N-methyltryptamine, 3) as a second end product. Our results demonstrate that mushrooms recruited distantly or entirely unrelated enzymes to evolve the metabolic capacity for 1 biosynthesis twice independently.