A vacuolar class III peroxidase and the metabolism of anticancer indole aklaloids in Catharanthus roseus

Abstract

Plants possess a unique metabolic diversity commonly designated as secondary metabolism, of which the anticancer alkaloids from Catharanthus roseus are among the most studied. Recently, in a classical function-to-protein-to-gene approach, we have characterized the main class III peroxidase (Prx) expressed in C. roseus leaves, CrPrx1, implicated in a key biosynthetic step of the anticancer alkaloids. We have shown the vacuolar sorting determination of CrPrx1 using GFP fusions and we have obtained further evidence supporting the role of this enzyme in alkaloid biosynthesis, indicating the potential of CrPrx1 as a molecular tool for the manipulation of alkaloid metabolism. Here, we discuss how plant cells may regulate Prx reactions. In fact, Prxs form a large multigenic family whose members accept a broad range of substrates and, in their two subcellular localizations, the cell wall and the vacuole, Prxs co-locate with a large variety of secondary metabolites which can be accepted as substrates. How then, are Prx reactions regulated? Localization data obtained in our lab suggest that arabinogalactan proteins (AGPs) and Prxs may be associated in membrane microdomains, evocative of lipid rafts. Whether plasma membrane and/or tonoplast microcompartmentation involve AGPs and Prxs and whether this enables metabolic channeling determining Prx substrate selection are challenging questions ahead.

Addendum to: Costa MM, Hilliou F, Duarte P, Pereira LG, Almeida I, Leech M, Memelink J, Barceló AR, Sottomayor M. Molecular cloning and characterization of a vacuolar class III peroxidase involved in the metabolism of anticancer alkaloids in Catharanthus roseus. Plant Physiol 2008; 146:403-17.

Figures and Tables

Figure 1 Biosynthesis of vinblastine from the monomeric precursors catharanthine and vindoline. Anhydrovinblastine is the product of the dimerization reaction and the precursor of the anticancer drugs vinblastine and vincristine.

Figure 2 (A) Cytochemical localization of CrPrx1 in C. roseus mesophyll cells using DAB and H₂O₂. (B) Green—immunofluorescence localization of AGPs using MAB Jim13 in C. roseus mesophyll cells. Blue—cell walls stained with calcofluor. Red—chloroplast autofluorescence. Bar = 4 µm.

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