Aureusidin synthase

[1] These pigments may have been developed to attract and guide bees for pollination,[5] but they also provide protection from viruses, pests and fungus.

Aureusidin synthase is homologous to plant polyphenol oxidase (PPO),[1] but contains certain significant modifications.

Much like PPOs,[8] aureusidin synthase is likely first synthesized as a larger ~60 kDa protein and then undergoes proteolytic cleavage to remove transport groups.

[1] Aureusidin synthase catalyzes the creation of aurones from chalcones through hydroxylation and oxidative cyclization.

From this and the protein's homology with PPO, the current proposed mechanism for aureusidin synthase is shown in Fig.

[11] The genetic modification of flowering plants to express colors not possible by natural breeding has been one of the main goals of the floricultural industry.

[4] This is accomplished by coexpressing Aureusidin synthase and UDP-glucose:chalcone 4'-O-glucosyltransferase in flowers and using RNA interference to block the expression of natural pigment production.

Chalcone and aurone images.
Fig. 1: (a) Generalized form of a chalcone. (b) Generalized form of an aurone. (c) Chalcone with the necessary modifications (2'- and 4-hydroxylation) to be processed by aureusidin synthase.
Fig 2: Generalized mechanism of aureusidin synthase. B denotes a base. In step 1, the 3 position is hydroxylated if necessary and both hydroxyl groups on the B-ring are oxidized. The second step is an oxidative cyclization, and step 3 is an isomerization.