Investigations of the biosynthesis of the phytotoxin coronatine

Abstract

Can. J. Chem. 72,86 (1994). The biosynthesis of the phytotoxin coronatine has been investigated by administration of isotopically labeled precursors to Pseudomonas syrirlgae pv. glycinea. The structure of coronatine contains two moieties of distinct biosynthetic origin, a bicyclic, hydrindanone carboxylic acid (coronafacic acid) and a cyclopropyl a-amino acid (coronamic acid). Investigations of coronafacic acid biosynthesis have shown that this compound is a polyketide derived from three acetate units, one butyrate unit, and one pyruvate unit. The two carbonyl oxygen atoms of coronafacic acid were found to be derived from the oxygen atoms of acetate. Additional experiments are described that rule out some possible modes for assembly of the polyketide chain. Coronamic acid is shown to be derived from L-isoleucine via the intermediacy of L-alloisoleucine. Examination of the mechanism of the cyclization of L-alloisoleucine to coronamic acid revealed that the formation of the cyclopropane ring takes place with the removal of only two hydrogen atoms from the amino acid, one at C-2 and the other at C-6. The nitrogen atom at C-2 of L-alloisoleucine is shown to be retained. On the basis of these observations, a mechanism is postulated for the cyclization reaction that involves the diversion of an enzymatic hydroxylation reaction into an oxidative cyclization. Finally, a precursor incorporation experiment with deuterium-labeled coronamic acid demonstrated that free coronamic acid can be efficiently incorporated into coronatine. This observation indicates that the cyclization of L-alloisoleucine to coronamic acid can occur before formation of the amide bond between coronafacic acid and coronamic acid. Can. J. Chem. 72,86 (1994). On a ktudik la biosynthkse de la phytotoxine coronatine en administrant des prtcurseurs marquks au Pseudort~onas syringae pv. glycinea. La structure de la coronatine contient deux portions d'origines biosynthktiques diffkrentes : un acide hydrindanone carboxylique bicyclique (l'acide coronafacique) et un acide cyclopropylique a-amink (I'acide coronamique). Des ktudes sur la biosynthkse de l'acide coronafacique ont montrk que ce composk est un polycktide dkrivk de trois unitks acktique, d'une unit6 butyrique et d'une unitt pyruvique. On a trouvk que les deux atomes d'oxygene carbonyles de I'acide coronafacique sont dtrivks des atomes d'oxygkne de l'acide acktique. On dkcrit des expkriences additionnelles qui permettent d'tliminer un certain nombre de modes d'assemblage de la chaine polycktide. On dkmontre que l'acide coronamique est dkrivk de la L-isoleucine par le biais de la L-alloisoleucine comme intermkdiaire. L'examen du mkcanisme de cyclisation de la L-alloisoleucine en acide coronamique a rkvklt que la formation du cyclopropane se produit avec l'enlkvement de seulement deux atomes d'hydrogene B partir de l'acide amink, I'un en C-2 et I'autre en C-6. On a dkmontrk que l'atome d'azote en C-2 de la L-alloisoleucine est conservk. Sur la base de ces observations, on propose un mkcanisme pour la r...

Biosynthesis of the Pseudomonas polyketide coronafacic acid requires monofunctional and multifunctional polyketide synthase proteins

“…Analysis of a cfa9 mutant indicated that this gene is dispensable for CFA and COR production but may increase the release of enzyme-bound products from the COR pathway (20). Precursor feeding studies with 13 C-labeled substrates demonstrated that CFA is a novel polyketide synthesized from C-2 and C-3 of pyruvate, three acetate units, and one butyrate unit (7). Further studies indicated that the pyruvate used for CFA biosynthesis is converted to ␣-ketoglutarate before incorporation into CFA (38).…”

Topological and deletion analysis of CorS, a Pseudomonas syringae sensor kinase

“…glycinea PG4180, which causes bacterial blight of soybeans (Budde et al, 1998;Palmer & Bender, 1993;Ullrich et al, 1995). Structurally, COR resembles a polyketide, and consists of two distinct moieties, coronafacic acid (CFA) and coronamic acid (CMA), which function as intermediates in the biosynthetic pathway to COR and are fused together by an amide bond (Mitchell et al, 1994;Parry et al, 1994). PG4180 produces COR predominantly at 18 u C, whereas there is no detectable COR production at 28 uC.…”

Characterization of CmaA, an Adenylation-Thiolation Didomain Enzyme Involved in the Biosynthesis of Coronatine

“…1). These two moieties are produced by different biosynthetic pathways (26). Three acetate units, one butyrate unit, and a four-carbon unit that is derived from glutamic acid are combined to form CFA (27), while CMA is derived from L-isoleucine via L-allo-isoleucine which is oxidatively cyclized to form the cyclopropane ring (25).…”