Structure-function studies of tetrahydroprotoberberine -methyltransferase reveal the molecular basis of stereoselective substrate recognition.

Benzylisoquinoline alkaloids (BIAs) are a structurally diverse class of plant-specialized metabolites that have been particularly well-studied in the order Ranunculales. The -methyltransferases (NMTs) in BIA biosynthesis can be divided into three groups according to substrate specificity and amino acid sequence. Here, we report the first crystal structures of enzyme complexes from the tetrahydroprotoberberine NMT (TNMT) subclass, specifically for TNMT from the yellow horned poppy ().