Enzymatic thioglycosylation: current knowledge and challenges - Carbohydrate Chemistry: Chemical and Biological Approaches - page 180

Cysteine. SunS exhibited relaxed substrate specificity for sugar donor,
as the authors could generate several glycosylated analogues using UDP-
a- D -N-acetylglucosamine, UDP-a- D -galactose, GDP-a- D -mannose, and
UDP-a- D -xylose as activated donors. The potentiality of using SunS to
biosynthesize sublancin peptidic analogues was further investigated by
structure-activity relationship of the peptide substrate towards SunS en-
zymatic activity. 17
Glycocin F, secreted by Lactobacillus plantarum KW30, was character-
ized and led to the identification of an unexpected N-acetylglucosamine
bound to a Cysteine by a thioglycosidic linkage. 18 Further studies by
structural nuclear magnetic resonance confirmed the presence of two N-
acetylglucosamine moieties, one attached to a Serine oxygen atom, the
second to a Cysteine sulfur atom. 19
1.2 Plant glucosinolates
Glucosinolates are plant secondary metabolites largely found in the order
Brassicales, which includes the Brassica crops, and the model plant
Arabidopsis thaliana. They have long been of interest to human society
because of their role in flavor and taste of Brassicaceae vegetables or
condiments. The main role of glucosinolates in plants is the defence
against herbivores, insects or microbial attacks. 20 Following cellular
disruption, glucosinolates are hydrolyzed by myrosinase, a b-thioglyco-
sidase 21 (GH1, EC 3.2.1.147), and produce an array of products that are
toxic to animals or bacteria, and are responsible for the flavor of the
plants but also have been identified as cancer-preventive compounds,
such as sulforaphane (Fig. 3). 22-26
These compounds are synthesized endogenously from three classes
of aminoacids, which require three separated metabolic pathways. 27
The biosynthesis pathway can be divided in three independent
Fig. 3 Biosynthesis and metabolism of glucosinolates.