TY - JOUR
T1 - Identification of iridoid synthases from Nepeta species
T2 - Iridoid cyclization does not determine nepetalactone stereochemistry
AU - Sherden, Nathaniel H.
AU - Lichman, Benjamin
AU - Caputi, Lorenzo
AU - Zhao, Dongyan
AU - Kamileen, Mohamed O.
AU - Buell, C. Robin
AU - O'Connor, Sarah E.
N1 - ©2017 The Author(s).
PY - 2018/1/1
Y1 - 2018/1/1
N2 - Nepetalactones are iridoid monoterpenes with a broad range of biological activities produced by plants in the Nepeta genus. However, none of the genes for nepetalactone biosynthesis have been discovered. Here we report the transcriptomes of two Nepeta species, each with distinctive profiles of nepetalactone stereoisomers. As a starting point for investigation of nepetalactone biosynthesis in Nepeta, these transcriptomes were used to identify candidate genes for iridoid synthase homologs, an enzyme that has been shown to form the core iridoid skeleton in several iridoid producing plant species. Iridoid synthase homologs identified from the transcriptomes were cloned, heterologously expressed, and then assayed with the 8-oxogeranial substrate. These experiments revealed that catalytically active iridoid synthase enzymes are present in Nepeta, though there are unusual mutations in key active site residues. Nevertheless, these enzymes exhibit similar catalytic activity and product profile compared to previously reported iridoid synthases from other plants. Notably, four nepetalactone stereoisomers with differing stereochemistry at the 4α and 7α positions – which are generated during the iridoid synthase reaction – are observed at different ratios in various Nepeta species. This work strongly suggests that the variable stereochemistry at these 4α and 7α positions of nepetalactone diastereomers is established further downstream in the iridoid pathway in Nepeta. Overall, this work provides a gateway into the biosynthesis of nepetalactones in Nepeta.
AB - Nepetalactones are iridoid monoterpenes with a broad range of biological activities produced by plants in the Nepeta genus. However, none of the genes for nepetalactone biosynthesis have been discovered. Here we report the transcriptomes of two Nepeta species, each with distinctive profiles of nepetalactone stereoisomers. As a starting point for investigation of nepetalactone biosynthesis in Nepeta, these transcriptomes were used to identify candidate genes for iridoid synthase homologs, an enzyme that has been shown to form the core iridoid skeleton in several iridoid producing plant species. Iridoid synthase homologs identified from the transcriptomes were cloned, heterologously expressed, and then assayed with the 8-oxogeranial substrate. These experiments revealed that catalytically active iridoid synthase enzymes are present in Nepeta, though there are unusual mutations in key active site residues. Nevertheless, these enzymes exhibit similar catalytic activity and product profile compared to previously reported iridoid synthases from other plants. Notably, four nepetalactone stereoisomers with differing stereochemistry at the 4α and 7α positions – which are generated during the iridoid synthase reaction – are observed at different ratios in various Nepeta species. This work strongly suggests that the variable stereochemistry at these 4α and 7α positions of nepetalactone diastereomers is established further downstream in the iridoid pathway in Nepeta. Overall, this work provides a gateway into the biosynthesis of nepetalactones in Nepeta.
KW - Iridoid
KW - Natural product biosynthesis
KW - Short chain alcohol dehydrogenase
KW - Terpenoid
UR - http://www.scopus.com/inward/record.url?scp=85032291510&partnerID=8YFLogxK
U2 - 10.1016/j.phytochem.2017.10.004
DO - 10.1016/j.phytochem.2017.10.004
M3 - Article
C2 - 29091815
AN - SCOPUS:85032291510
SN - 0031-9422
VL - 145
SP - 48
EP - 56
JO - PHYTOCHEMISTRY
JF - PHYTOCHEMISTRY
ER -