Epithiospecifier proteins

Figure 13.1 Degradation of glucosinolates. Hydrolysis is catalyzed by myrosinases and gives rise to different degradation products dependent on the structure of the glucosinolate side chain and the hydrolysis conditions. (I) isothiocyanates, the major product at pH >7 (II) nitriles, the major product at pH <4 (ID) thiocyanates, produced from 2-propenyl-, benzyl-, and 4-methylthiobutylglucosinolates (IV) oxazolidine-2-thiones, produced from glucosinolates with P-hydroxylated side chains, (V) epithionitriles, produced in the presence of epithiospecifier proteins.

Lambrix V, Reichelt M, Mitchell-Olds T, Kliebenstein DJ, Gershenzon J (2001) The Arabidopsis epithiospecifier protein promotes the hydrolysis of glucosinolates to nitriles and influences Trichoplusia ni herbivory. Plant cell 13 2793-2807... 

Matusheski NV, Swamp R, Juvik JA, Mithen R, Bennett M, Jeffery EH (2006) Epithiospecifier protein from broccoli Brassica oleracea L. ssp. Italica) inhibits formation of the anticancer agent sulforaphane. J Agric Food Chem 54 2069-2076... 

An Arabidopsis thaliana Epithiospecifier Protein (ESP) Alters Glucosinolate... 

A major proportion of the glucosinolate hydrolysis products formed upon myrosinase cleavage in some plants are nitriles. In vitro, nitrile formation associated with myrosinase-catalyzed hydrolysis is enhanced at low pH (pH<3) and in the presence of ferrous ions. In vivo, protein factors in addition to myrosinase may be responsible for nitrile formation. If the glucosinolate side chain has a terminal double bond, the sulfur released from the thioglucosidic bond may be captured by the double bond and an epithionitrile is formed.9 This reaction takes place only in plants that possess a protein factor known as epithiospecifier protein (ESP). ESP activities have been identified in several species of the Brassicaceae and shown to influence the outcome of the myrosinase-catalvzed hydrolysis reaction although they have no hydrolytic activity by themselves.10 12 The mechanism by which ESPs promote epithionitrile formation is not known. 

AN ARABIDOPSIS THALIANA EPITHIOSPECIFIER PROTEIN (ESP) ALTERS GLUCOSINOLATE HYDROLYSIS... 

PETROSKI, R.J., TOOKEY, H.L., Interactions of thioglucoside glucohydrolase and epithiospecifier protein of cruciferous plants to form 1-cyanoepithioalkanes., Phytochemistry, 1982,21, 1903-1905. 

MACLEOD, A.J., ROSSITER, J.T., The occurence and activity of epithiospecifier protein in some Cruciferae seeds., Phytochemistry, 1985,24,1895-1898. 

BERNARDI, R., NEGRI, A., RONCM, S., PALMIERI, S., Isolation of the epithiospecifier protein from oil-rape (Brassica napus ssp oleifera) seed and its characterization., FEBSLett., 2000,467,296-298. 

The reaction products depend on pH and other factors such as the presence of ferrous ions, epithiospecifier protein, and the nature of the glucosinolate side chain. Epithiospecifier protein has recently been independently purified and characterized7,8 and appears to require ferrous ions indicating the formation of an organometallic (FeN - aglycone) intermediate that leads to die formation of a thiirane ring. 

GSL aglycones may yield a nitrile rather than an ITC under certain conditions, like a low pH and the presence of a protein similar to the epithiospecifier protein (ESP) that has been characterized in B. napus and Arabidopsis thaliana (Lambrix etal 2001 Matusheski etal 2004 Neugart et al. 2012). The production of nitriles as opposed to ITC impacts negatively on the anticancer potential of these vegetables. It appears that ITCs are more potent inducers compared to allyl nitriles and their activity is expressed in a wider range of tissues (Tanii etal. 2005). However, few works have studied the chemopreventive effect of GSL-derived nitriles. Among the known cruciferous nitriles, the most studied are nitrile crambene, sulforaphane nitrile, and allyl nitrile. 

Lambrix, V., Reichelt, M., Mitchell-Olds, T., Kliebenstein, D.J., and Gershenzon, J. 2001. The Arabidopsis Epithiospecifier Protein Promotes the Hydrolysis of Glucosinolates to Nitriles and Influences Trichoplusiani Herbivory. Plant Cell, I3( 2), 2793-2807. doi 10.1105/tpc.010261. 

Matusheski, N.V., Juvik, J.A., and Jeffery, E.H. 2004. Heating decreases epithiospecifier protein... 

Foo, H.L. et al. (2000) Purification and characterisation of epithiospecifier protein from Brassica napus enzymic intramolecular sulphur addition within alkenyl thiohydroximates derived from alkenyl glucosinolate hydrolysis. FEBSLett 468 (2-3), 243-246... 

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