StnK2 catalysing a Pictet–Spengler reaction involved in the biosynthesis of the antitumor reagent streptonigrin

StnK2 is a new Pictet–Spenglerase specifically catalyzing a (1R,3S,4S)-tetrahydro-β-carboline scaffold as the biosynthetic intermediate of the antitumor reagent streptonigrin.