Distinct substrate specificities and unusual substrate flexibilities of two hydroxycinnamoyltransferases,rosmarinic acid synthase and hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyl-transferase,from <Emphasis Type="Italic">Coleus blumei</Emphasis> Benth. |
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Authors: | Marion?Sander Email author" target="_blank">Maike?PetersenEmail author |
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Institution: | 1.Institut für Pharmazeutische Biologie und Biotechnologie,Philipps-Universit?t Marburg,Marburg,Germany |
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Abstract: | cDNAs and genes encoding a hydroxycinnamoyl-CoA:hydroxyphenyllactate hydroxycinnamoyltransferase (CbRAS; rosmarinic acid synthase)
and a hydroxycinnamoyl-CoA:shikimate hydroxycinnamoyltransferase (CbHST) were isolated from Coleus blumei Benth. (syn. Solenostemon scutellarioides (L.) Codd; Lamiaceae). The proteins were expressed in E. coli and the substrate specificity of both enzymes was tested. CbRAS accepted several CoA-activated phenylpropenoic acids as donor
substrates and d-(hydroxy)phenyllactates as acceptors resulting in ester formation while shikimate and quinate were not accepted. Unexpectedly,
amino acids (d-phenylalanine, d-tyrosine, d-DOPA) also yielded products, showing that RAS can putatively catalyze amide formation. CbHST was able to transfer cinnamic,
4-coumaric, caffeic, ferulic as well as sinapic acid from CoA to shikimate but not to quinate or acceptor substrates utilized
by CbRAS. In addition, 3-hydroxyanthranilate, 3-hydroxybenzoate and 2,3-dihydroxybenzoate were used as acceptor substrates.
The reaction product with 3-aminobenzoate putatively is an amide. For both enzymes, structural requirements for donor and
acceptor substrates were deduced. The acceptance of unusual acceptor substrates by CbRAS and CbHST resulted in the formation
of novel compounds. The rather relaxed substrate as well as reaction specificity of both hydroxycinnamoyltransferases opens
up possibilities for the evolution of novel enzymes forming novel secondary metabolites in plants and for the in vitro formation
of new compounds with putatively interesting biological activities. |
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