Poster: Enzymology
Abs #
242: Barley agmatine coumaroyltransferase in cinnamic acid amide biosynthesis
Agmatine coumaroyltransferase (ACT) combines the primary polyamine pathway and the secondary phenylpropanoid pathway. It catalyses the synthesis of hydroxycinnamoylagmatines (HCA) from agmatine and p-hydroxycinnamoyl-CoA thiolesters in barley (H. vulgare). The HCA’s are direct precursor of the antifungal compound hordatine, which seems to be confined to the genus Hordeum as preformed infectional inhibitor. However, recent studies indicate that the syntheses of HCA derivatives are induced in response to fungal infection of the leaves. Additionally, HCA derivatives have been found in wheat, and histochemical staining of infected epidermal leaf tissue confirms that these compounds might accumulate in cereals in general. ACT was purified to apparent homogeneity from barley seedlings (1). The enzyme was highly specific for agmatine as acyl acceptor and had the highest specificity for p-coumaroyl-CoA among various acyl donors. It was found to be a single polypeptide chain of 48 kDa with a pI of 5.2. The 15 N-terminal amino acid residues were identified and used to clone a full-length barley ACT cDNA that predicted a protein of 439 amino acid residues. The sequence was devoid of N-terminal signal peptide suggesting a cytosolic localisation. Recombinant ACT produced and affinity-purified from E. coli showed high specific ACT activity, thus confirming the identity of the purified native protein. A partial cDNA sequence for ACT was obtained from wheat, which predicted a protein of 353 amino acid residues, and had 95% sequence identity to barley ACT. Two motifs in the amino acid sequence reveal that barley ACT represents a new class of N-hydroxycinnamoyltransferases belonging to the diverse transferase superfamily.
(1) Burhenne et al. (2003) J Biol Chem, in press.
