6j1m

Publication Abstract from PubMed

The skeleton of tropane alkaloids is derived from ornithine-derived N-methylpyrrolinium and two malonyl-CoA units. The enzymatic mechanism that connects N-methylpyrrolinium and malonyl-CoA units remains unknown. Here, we report the characterization of three pyrrolidine ketide synthases (PYKS), AaPYKS, DsPYKS, and AbPYKS, from three different hyoscyamine- and scopolamine-producing plants. By examining the crystal structure and biochemical activity of AaPYKS, we show that the reaction mechanism involves PYKS-mediated malonyl-CoA condensation to generate a 3-oxo-glutaric acid intermediate that can undergo non-enzymatic Mannich-like condensation with N-methylpyrrolinium to yield the racemic 4-(1-methyl-2-pyrrolidinyl)-3-oxobutanoic acid. This study therefore provides a long sought-after biosynthetic mechanism to explain condensation between N-methylpyrrolinium and acetate units and, more importantly, identifies an unusual plant type III polyketide synthase that can only catalyze one round of malonyl-CoA condensation.

Tropane alkaloids biosynthesis involves an unusual type III polyketide synthase and non-enzymatic condensation.,Huang JP, Fang C, Ma X, Wang L, Yang J, Luo J, Yan Y, Zhang Y, Huang SX Nat Commun. 2019 Sep 6;10(1):4036. doi: 10.1038/s41467-019-11987-z. PMID:31492848^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.