EC 1.3.1.122     
Accepted name: (S)-8-oxocitronellyl enol synthase
Reaction: (S)-8-oxocitronellyl enol + NAD(P)+ = (6E)-8-oxogeranial + NAD(P)H + H+
Glossary: (S)-8-oxocitronellyl enol = (2E,6S,7E)-8-hydroxy-2,6-dimethylocta-2,7-dienal
Other name(s): CrISY; 8-oxogeranial:NAD(P)+ oxidoreductase (cyclizing, cis-trans-nepetalactol forming); iridoid synthase (incorrect)
Systematic name: (S)-8-oxocitronellyl enol:NAD(P)+ oxidoreductase
Comments: Isolated from the plants Catharanthus roseus, Olea europaea (common olive), and several Nepeta species. The enzyme reduces 8-oxogeranial, generating an unstable product that is subsequently cyclized into several possible products, either non-enzymically or by dedicated cyclases. The products, known as iridoids, are involved in the biosynthesis of many indole alkaloids. cf. EC 1.3.1.123, 7-epi-iridoid synthase.
References:
1.  Geu-Flores, F., Sherden, N.H., Courdavault, V., Burlat, V., Glenn, W.S., Wu, C., Nims, E., Cui, Y. and O'Connor, S.E. An alternative route to cyclic terpenes by reductive cyclization in iridoid biosynthesis. Nature 492 (2012) 138–142. [PMID: 23172143]
2.  Hu, Y., Liu, W., Malwal, S.R., Zheng, Y., Feng, X., Ko, T.P., Chen, C.C., Xu, Z., Liu, M., Han, X., Gao, J., Oldfield, E. and Guo, R.T. Structures of iridoid synthase from Catharanthus roseus with bound NAD(+) , NADPH, or NAD(+) /10-oxogeranial: Reaction mechanisms. Angew. Chem. Int. Ed. Engl. 54 (2015) 15478–15482. [PMID: 26768532]
3.  Alagna, F., Geu-Flores, F., Kries, H., Panara, F., Baldoni, L., O'Connor, S.E. and Osbourn, A. Identification and characterization of the iridoid synthase involved in oleuropein biosynthesis in olive (Olea europaea) fruits. J. Biol. Chem. 291 (2016) 5542–5554. [PMID: 26709230]
4.  Qin, L., Zhu, Y., Ding, Z., Zhang, X., Ye, S. and Zhang, R. Structure of iridoid synthase in complex with NADP+/8-oxogeranial reveals the structural basis of its substrate specificity. J. Struct. Biol. 194 (2016) 224–230. [PMID: 26868105]
5.  Sherden, N.H., Lichman, B., Caputi, L., Zhao, D., Kamileen, M.O., Buell, C.R. and O'Connor, S.E. Identification of iridoid synthases from Nepeta species: Iridoid cyclization does not determine nepetalactone stereochemistry. Phytochemistry 145 (2018) 48–56. [PMID: 29091815]
6.  Lichman, B.R., Kamileen, M.O., Titchiner, G.R., Saalbach, G., Stevenson, C.EM., Lawson, D.M. and O'Connor, S.E. Uncoupled activation and cyclization in catmint reductive terpenoid biosynthesis. Nat. Chem. Biol. 15 (2019) 71–79. [PMID: 30531909]
7.  Lichman, B.R., O'Connor, S.E. and Kries, H. Biocatalytic strategies towards [4+2] cycloadditions. Chemistry 25 (2019) 6864–6877. [PMID: 30664302]
[EC 1.3.1.122 created 2013 as EC 1.3.1.99, part transferred 2019 to EC 1.3.1.122]
 
 


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