A cane toad (Rhinella marina) N-methyltransferase converts primary indolethylamines to tertiary psychedelic amines.

A novel indolethylamine N-methyltransferase (RmNMT) from the cane toad (Rhinella marina) was identified and characterized. This enzyme catalyzes the biosynthesis of psychedelic alkaloids such as DMT, 5-methoxy-DMT, and bufotenin, which accumulate in toad skin and parotid glands and have been used ceremonially by Mesoamerican peoples. RmNMT is an effective catalyst not subject to product inhibition and exhibits substrate promiscuity, enabling production of various substituted indolethylamines for purification, pharmacological screening, and metabolic stability assays. Binding evaluations at serotonin receptors showed that primary amines have enhanced affinity at the 5-HT1A receptor compared with tertiary amines. Except for 6-substituted derivatives, N,N-dimethylation protected against catabolism by liver microsomes.

Study at a glance

Abstract

Psychedelic indolethylamines have emerged as potential medicines to treat several psychiatric pathologies. Natural sources of these compounds include 'magic mushrooms' (Psilocybe spp.), plants used to prepare ayahuasca, and toads. The skin and parotid glands of certain toads accumulate a variety of specialized metabolites including toxic guanidine alkaloids, lipophilic alkaloids, poisonous steroids, and hallucinogenic indolethylamines such as DMT, 5-methoxy-DMT, and bufotenin. The occurrence of psychedelics has contributed to the ceremonial use of toads, particularly among Mesoamerican peoples. Yet, the biosynthesis of psychedelic alkaloids has not been elucidated. Herein, we report a novel indolethylamine N-methyltransferase (RmNMT) from cane toad (Rhinella marina). The RmNMT sequence was used to identify a related NMT from the common toad, Bufo bufo. Close homologs from various frog species were inactive, suggesting a role for psychedelic indolethylamine biosynthesis in toads. Enzyme kinetic analyses and comparison with functionally similar enzymes showed that recombinant RmNMT was an effective catalyst and not product inhibited. The substrate promiscuity of RmNMT enabled the bioproduction of a variety of substituted indolethylamines at levels sufficient for purification, pharmacological screening, and metabolic stability assays. Since the therapeutic potential of psychedelics has been linked to activity at serotonergic receptors, we evaluated binding of derivatives at 5-HT1A and 5-HT2A receptors. Primary amines exhibited enhanced affinity at the 5-HT1A receptor compared with tertiary amines. With the exception of 6-substituted derivatives, N,N-dimethylation also protected against catabolism by liver microsomes.