The Enzyme Database

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Transferred entry: iridoid synthase. Now known to be catalyzed by two different enzymes, EC, (S)-8-oxocitronellyl enol synthase, and EC, (+)-cis,trans-nepetalactol synthase
[EC created 2013, deleted 2019]
Accepted name: (S)-8-oxocitronellyl enol synthase
Reaction: (S)-8-oxocitronellyl enol + NAD(P)+ = (6E)-8-oxogeranial + NAD(P)H + H+
For diagram of secologanin biosynthesis, click here
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, 7-epi-iridoid synthase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
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. [DOI] [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 created 2013 as EC, part transferred 2019 to EC]
Accepted name: oleuropein β-glucosidase
Reaction: oleuropein + H2O = oleuropein aglycone + D-glucopyranose
Glossary: oleuropein aglycone = methyl (2S,3E,4S)-4-{2-[2-(3,4-dihydroxyphenyl)ethoxy]-2-oxoethyl}-3-ethylidene-2-hydroxy-3,4-dihydro-2H-pyran-5-carboxylate
oleuropein = methyl (2R,3E,4S)-4-{2-[2-(3,4-dihydroxyphenyl)ethoxy]-2-oxoethyl}-3-ethylidene-2-(β-D-glucopyranosyloxy)-3,4-dihydro-2H-pyran-5-carboxylate
ligstroside = methyl (2S,3E,4S)-3-ethylidene-2-(β-D-glucopyranosyloxy)-4-{2-[2-(4-hydroxyphenyl)ethoxy]-2-oxoethyl}-3,4-dihydro-2H-pyran-5-carboxylate
Other name(s): OeGLU (gene name)
Systematic name: oleuropein 2-β-D-glucohydrolase
Comments: Oleuropein is a glycosylated secoiridoid exclusively biosynthesized by members of the Oleaceae plant family where it is part of a defence system againt herbivores. The enzyme also hydrolyses ligstroside and demethyloleuropein.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
1.  Ciafardini, G., Marsilio, V., Lanza, B. and Pozzi, N. Hydrolysis of oleuropein by Lactobacillus plantarum strains associated with olive fermentation. Appl. Environ. Microbiol. 60 (1994) 4142–4147. [PMID: 16349442]
2.  Romero-Segura, C., Sanz, C. and Perez, A.G. Purification and characterization of an olive fruit β-glucosidase involved in the biosynthesis of virgin olive oil phenolics. J. Agric. Food Chem. 57 (2009) 7983–7988. [DOI] [PMID: 19689134]
3.  Gutierrez-Rosales, F., Romero, M.P., Casanovas, M., Motilva, M.J. and Minguez-Mosquera, M.I. β-Glucosidase involvement in the formation and transformation of oleuropein during the growth and development of olive fruits (Olea europaea L. cv. Arbequina) grown under different farming practices. J. Agric. Food Chem. 60 (2012) 4348–4358. [DOI] [PMID: 22475562]
4.  Koudounas, K., Banilas, G., Michaelidis, C., Demoliou, C., Rigas, S. and Hatzopoulos, P. A defence-related Olea europaea β-glucosidase hydrolyses and activates oleuropein into a potent protein cross-linking agent. J. Exp. Bot. 66 (2015) 2093–2106. [DOI] [PMID: 25697790]
5.  Koudounas, K., Thomopoulou, M., Michaelidis, C., Zevgiti, E., Papakostas, G., Tserou, P., Daras, G. and Hatzopoulos, P. The C-domain of oleuropein β-glucosidase assists in protein folding and sequesters the enzyme in nucleus. Plant Physiol. 174 (2017) 1371–1383. [DOI] [PMID: 28483880]
[EC created 2017]

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