Structures of Iridoid Synthase From Cantharanthus Roseus With Bound NAD(+) , NADPH, or NAD(+) /10-Oxogeranial: Reaction Mechanisms

Angew Chem Int Ed Engl. 2015 Dec 14;54(51):15478-15482. doi: 10.1002/anie.201508310. Epub 2015 Nov 13.


Structures of the iridoid synthase nepetalactol synthase in the presence of NAD(+) , NADPH or NAD(+) /10-oxogeranial were solved. The 10-oxogeranial substrate binds in a transoid-O1-C3 conformation and can be reduced by hydride addition to form the byproduct S-10-oxo-citronellal. Tyr178 Oζ is positioned 2.5 Å from the substrate O1 and provides the second proton required for reaction. Nepetalactol product formation requires rotation about C1-C2 to form the cisoid isomer, leading to formation of the cis-enolate, together with rotation about C4-C5, which enables cyclization and lactol production. The structure is similar to that of progesterone-5β-reductase, with almost identical positioning of NADP, Lys146(147), Tyr178(179), and F342(343), but only Tyr178 and Phe342 appear to be essential for activity. The transoid 10-oxogeranial structure also serves as a model for β-face hydride attack in progesterone 5β-reductases and is of general interest in the context of asymmetric synthesis.

Keywords: X-ray crystallography; biosynthesis; enzyme mechanisms; monoterpenes; natural products.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acyclic Monoterpenes
  • Apocynaceae / enzymology*
  • Iridoids / chemistry*
  • Ligases / chemistry*
  • Models, Molecular
  • Molecular Structure
  • Monoterpenes / chemistry*
  • NAD / chemistry*
  • NADP / chemistry*


  • Acyclic Monoterpenes
  • Iridoids
  • Monoterpenes
  • NAD
  • NADP
  • Ligases
  • citral