Strictosidine Glucosidase SG

SG and raucaffricine glucosidase share a high degree of structural similarity. Both are members of the GH-1 superfamily. They are illustrated and compared in the paragraph on raucaffricine glucosidase later in Section 4.3.2. 

It seems that Hisl61 is not a catalytic amino acid, because it is far away from the anomeric Cl by a distance of about 5.8 A. But it may help to hold the substrate in the right geometry for hydrolysis by hydrogen bonding to 03 of the glucose moiety. 

In addition, binding residues of the hydrophobic moiety (indole moiety) are also mosdy hydrophobic. Of them Trp388 is of special interest, because it does not occupy that conformation in all other plant-derived glucosidases. The resulting changes in substrate specificity when compared with the second p-glucosidase of the pathway, i.e., raucaf icine glucosidase (RG), were described in Ref 95 and wiU be discussed later in this article. The most 

On the search for participating enzymes in the SB formation, compound 2, labeled at the C-5 position by was enzymatically prepared. 

However, under various conditions, soluble enzyme preparations did not catalyze sarpagan- or ajmalan-type alkaloid biosynthesis. In contrast, a ceU-free system consisting of crude, soluble protein mixed with microsomal protein led to the formation ofveUosimol (10-deoxysarpagine, 15) in the 

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Fig. 8.1 Sequence of reactions and pathways involved in the biosynthesis of indole alkaloids in Catharanthus roseus. The dotted lines indicate multiple and/or uncharacterized enzyme steps. Tryptophan decarboxylase (TDC), Geraniol Hydroxylase (GH), Deoxyloganin synthase (DS), Secologanin Synthase (SLS) Strictosidine synthase (STR1), Strictosidine glucosidase (SG), Tabersonine-16-hydroxylase (T16H), Tabersonine 6,7-eposidase (T6,7E), Desacetoxyvindoline-4-hydroxylase (D4H), Deacetyl-vindoline-4-O-acetyltransferase (DAT) and Minovincinine-19-O-acetyltransferase (MAT) represent some of the enzyme steps that have been characterized.

From strictosidine, the first step toward the various types of indole alkaloids is deglucosylation by strictosidine glucosidase (SG, EC 3.2.12). The key to the diversification in indole alkaloids must be at the glucosidase or in the steps directly after this enzyme. The glucosidase and the subsequent steps have thus been the subject of quite a few studies. 

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