Dual Catalytic Activity of Hydroxycinnamoyl-Coenzyme A Quinate Transferase from Tomato Allows It to Moonlight in the Synthesis of Both Mono- and Dicaffeoylquinic Acids    . Issue 4 (9th October 2014)

• Record Type: Journal Article
• Authors: Moglia, Andrea; Lanteri, Sergio; Comino, Cinzia; Hill, Lionel; Knevitt, Daniel; Cagliero, Cecilia; Rubiolo, Patrizia; Bornemann, Stephen; Martin, Cathie
• Is Part Of: Plant physiology. Volume 166:Issue 4(2014)
• Page Start: 1777
• Page End: 1787
• Publication Date: 2014-10-09
• Subjects: Plant physiology -- Periodicals; Botany -- Periodicals; Periodicals; Electronic journals; 571.2
• DOI: 10.1104/pp.114.251371
• Languages: English
• ISSNs: 0032-0889

Abstract

Abstract : A cytoplasmic enzyme known to synthesise chlorogenic acid in tomato has a second activity synthesising dicaffeoyl quinates at low pH and high chlorogenic acid concentrations in the vacuole . Abstract: Tomato ( Solanum lycopersicum ), like other Solanaceous species, accumulates high levels of antioxidant caffeoylquinic acids, which are strong bioactive molecules and protect plants against biotic and abiotic stresses. Among these compounds, the monocaffeoylquinic acids (e.g. chlorogenic acid [CGA ]) and the dicaffeoylquinic acids (diCQA s) have been found to possess marked antioxidative properties. Thus, they are of therapeutic interest both as phytonutrients in foods and as pharmaceuticals. Strategies to increase diCQA content in plants have been hampered by the modest understanding of their biosynthesis and whether the same pathway exists in different plant species. Incubation of CGA with crude extracts of tomato fruits led to the formation of two new products, which were identified by liquid chromatography-mass spectrometry as diCQA s. This chlorogenate:chlorogenate transferase activity was partially purified from ripe fruit. The final protein fraction resulted in 388-fold enrichment of activity and was subjected to trypsin digestion and mass spectrometric sequencing: a hydroxycinnamoyl-Coenzyme A:quinate hydroxycinnamoyl transferase (HQT ) was selected as a candidate protein. Assay of recombinant HQT protein expressed in Escherichia coli confirmed its ability to synthesize diCQA s in vitro. This second activity (chlorogenate:chlorogenate transferase) of HQT had a low pH optimum and a high K m for its substrate, CGA . High concentrations of CGA and relatively low pH occur in the vacuoles of plant cells. Transient assays demonstrated that tomato HQT localizes to the vacuole as well as to the cytoplasm of plant cells, supporting the idea that in this species, the enzyme catalyzes different reactions in two subcellular compartments.