This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Degradation/Utilization/Assimilation → Secondary Metabolites Degradation → Nitrogen Containing Secondary Compounds Degradation → Nitrogen Containing Glucosides Degradation → Glucosinolates Degradation|
Some taxa known to possess this pathway include : Lepidium sativum
Expected Taxonomic Range: Brassicales
Glucosinolates are 1-thio-beta-D-glucosides. They are found prominently in the order Capparales, which include cabbage, mustard, oilseed rape, broccoli, and the model plant Arabidopsis. In addition to be responsible for the typical sharp taste and odor of many glucosinolate-producing plants, glucosinolates play an important role in plant defense. In plant herbivore defense, glucosinolates are hydrolyzed and broken down to toxic compounds by the myrosinase system. Myrosinases are S-glycosidases. They are the only known S-glycosidases. Isothiocyanate, automatically formed from the myrosinase product glucosinolate aglycone (thiohydroximate-O-sulfate), is bioactive. It has been shown to have antimicrobial and insecticidal activities. In addition to isothiocyanate, in the presence of specific plant proteins, glucosinolate hydrolysis products are diverted away from isothiocyanate. Epithiospecifier proteins (ESPs), previously characterized, are responsible for the formation simple nitrile or epithionitrile, depending on the structure of the parent glucosinolate (see glucosinolate breakdown). Recently, a thiocyanate-forming protein (TFP) has been cloned and characterized, which can divert glucosinolate hydrolysis to organic thiocyanate formation [Burow07]. In contrast to isothiocyanates, the ecological roles of nitriles and thiocyanates formed in the ESP/TSP system is still unclear. They are more likely to be involved in defense responses against insect herbivores rather than in those against pathogens (reviewed in [Burow09]).
About This Pathway
The production of organic thiocyanate upon glucosinolate hydrolysis is restricted to only a few plant species. Besides, only a few glucosinolates, namely benzylglucosinolate, allylglucosinolate and 4-methylthiobutylglucosinolate can be converted to organic thiocyanate by TFP. In Lepidium sativum, benzylglucosinolate is the major, if not only, glucosinolate found in the above-ground plant organs. Upon tissue damage, benzylglucosinolate is hydrolyzed to isothiocyanate, thiocyanate and simple nitrile. The formation of isothiocyanate from benzylglucosinolate aglycone is spontaneous, whereas the formation of thiocyanate and simple nitrile requires a thiocyanate-forming protein (TFP). TFP has been cloned from Lepidium sativum [Burow07]. It shares 63-68% amino acid sequence identity with known epithiospecifier proteins (ESPs).
The L. sativum TFP does not only catalyze thiocyanate and simple nitrile formation from benzylglucosinolate, but also the formation of simple nitrile and epithionitrile formation from ectopically supplied aliphatic glucosinolates [Burow07].
Burow07: Burow M, Bergner A, Gershenzon J, Wittstock U (2007). "Glucosinolate hydrolysis in Lepidium sativum--identification of the thiocyanate-forming protein." Plant Mol Biol 63(1);49-61. PMID: 17139450
Franz07: Franz B, Lichtenberg H, Hormes J, Modrow H, Dahl C, Prange A (2007). "Utilization of solid "elemental" sulfur by the phototrophic purple sulfur bacterium Allochromatium vinosum: a sulfur K-edge X-ray absorption spectroscopy study." Microbiology 153(Pt 4);1268-74. PMID: 17379736
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