Strictosichne synthase (sTRI) catalyzes the stereoselective formation of 3 alpha(S)-strictosidine from tryptamine and secologanin. Strictosidine is the key intermediate in the biosynthesis of 2,000 plant monoterpenoid indole alkaloids, and it is a key precursor of enzyme-mediated synthesis of alkaloids. An improved expression system is described which leads to optimized His(6)-STR1 synthesis in Escherichia coli. Optimal production of STRI was achieved by determining the impact of co-expression of chaperones pG-Tf2 and pG-LJES. The amount and activity of sTRI was doubled in the presence of chaperone pG-Tf2 alone. His(6)-STRI immobilized on Ni-NTA can be used for enzymatic synthesis of strictosidines on a preparative scale. With the newly co-expressed His(6)-STRI. novel 3 alpha(5)-12-azastrictosidine was obtained by enzymatic catalysis of 7-azatryptamine and secologanin. The results obtained are of significant importance for application to chemo-enzymatic approaches leading to diversification of alkaloids with novel improved structures.