Phenolic metabolism in the hornwort Anthoceros agrestis: 4-coumarate CoA ligase and 4-hydroxybenzoate CoA ligase.

4-Coumarate coenzyme A ligase and 4-hydroxybenzoate coenzyme A ligase from the hornwort Anthoceros agrestis expressed in E. coli were characterized on biochemical and molecular levels and showed interesting substrate specificities. Acyl-activating enzymes are associated with the biosynthesis or degradation of various metabolic products such as lipids, amino acids, sugars, and natural compounds. In this work, cDNA sequences encoding 4-coumarate coenzyme A ligase (4CL) and 4-hydroxybenzoate coenzyme A ligase (4HBCL) were amplified from the hornwort Anthoceros agrestis. The coding sequences were expressed in E. coli and purified by Ni-chelate chromatography. The CoA ligases exhibited different substrate specificities. 4CL catalyzed the activation of 4-coumaric acid, 3-coumaric acid, 2-coumaric acid, caffeic acid, isoferulic acid, ferulic acid, and cinnamic acid but lacked activities towards sinapic acid and benzoic acids. In contrast, 4HBCL preferred 4-hydroxybenzoic acid and benzoic acid, but also accepted other benzoic acid derivatives except salicylic acid and 3-aminosalicylic acid. Furthermore, 4HBCL also activated isoferulic acid, cinnamic acid, 2-coumaric acid, 3-coumaric acid, 4-coumaric acid and caffeic acid, but lacked affinity for ferulic acid and sinapic acid. These substrate specificities could be related to the phenolic compounds identified in Anthoceros agrestis.