Methyl transfer in psilocybin biosynthesis.

Psilocybin, the natural hallucinogen produced by Psilocybe ("magic") mushrooms, holds great promise for the treatment of depression and several other mental health conditions. The final step in the psilocybin biosynthetic pathway, dimethylation of the tryptophan-derived intermediate norbaeocystin, is catalysed by PsiM. Here we present atomic resolution (0.9 Å) crystal structures of PsiM trapped at various stages of its reaction cycle, providing detailed insight into the SAM-dependent methylation mechanism. Structural and phylogenetic analyses suggest that PsiM derives from epitranscriptomic N6-methyladenosine writers of the METTL16 family, which is further supported by the observation that bound substrates physicochemically mimic RNA. Inherent limitations of the ancestral monomethyltransferase scaffold hamper the efficiency of psilocybin assembly and leave PsiM incapable of catalysing trimethylation to aeruginascin. The results of our study will support bioengineering efforts aiming to create novel variants of psilocybin with improved therapeutic properties.

Structural and Biochemical Characterization of Staphylococcus aureus Cysteine Desulfurase Complex SufSU.

In this work, we provide the first in vitro characterization of two essential proteins from Staphylococcus aureus (S. aureus) involved in iron-sulfur (Fe-S) cluster biogenesis: the cysteine desulfurase SufS and the sulfurtransferase SufU. Together, these proteins form the transient SufSU complex and execute the first stage of Fe-S cluster biogenesis in the SUF-like pathway in Gram-positive bacteria. The proteins involved in the SUF-like pathway, such as SufS and SufU, are essential in Gram-positive bacteria since these bacteria tend to lack redundant Fe-S cluster biogenesis pathways. Most previous work characterizing the SUF-like pathway has focused on Bacillus subtilis (B. subtilis). We focus on the SUF-like pathway in S. aureus because of its potential to serve as a therapeutic target to treat S. aureus infections. Herein, we characterize S. aureus SufS (SaSufS) by X-ray crystallography and UV-vis spectroscopy, and we characterize S. aureus SufU (SaSufU) by a zinc binding fluorescence assay and small-angle X-ray scattering. We show that SaSufS is a type II cysteine desulfurase and that SaSufU is a Zn2+-containing sulfurtransferase. Additionally, we evaluated the cysteine desulfurase activity of the SaSufSU complex and compared its activity to that of B. subtilis SufSU. Subsequent cross-species activity analysis reveals a surprising result: SaSufS is significantly less stimulated by SufU than BsSufS. Our results set a basis for further characterization of SaSufSU as well as the development of new therapeutic strategies for treating infections caused by S. aureus by inhibiting the SUF-like pathway.