Homology modeling and dynamics study of aureusidin synthase--an important enzyme in aurone biosynthesis of snapdragon flower.

Aurones, a class of plant flavonoids, provide bright yellow color on some important ornamental flowers, such as cosmos, coreopsis, and snapdragon (Antirrhinum majus). Recently, it has been elucidated that aureusidin synthase (AUS), a homolog of plant polyphenol oxidase (PPO), plays a key role in the yellow coloration of snapdragon flowers. In addition, it has been shown that AUS is a chalcone-specific PPO specialized for aurone biosynthesis. AUS gene has been successfully demonstrated as an attractive tool to engineer yellow flowers in blue flowers. Despite these biological studies, the structural basis for the specificity of substrate interactions of AUS remains elusive. In this study, we performed homology modeling of AUS using Grenache PPO and Sweet potato catechol oxidase (CO). An AUS-inhibitor was then developed from the initial homology model based on the CO and subsequently validated. We performed a thorough study between AUS and PTU inhibitor by means of interaction energy, which indicated the most important residues in the active site that are highly conserved. Analysis of the molecular dynamics simulations of the apo enzyme and ligand-bound complex showed that complex is relatively stable than apo and the active sites of both systems are flexible. The results from this study provide very helpful information to understand the structure-function relationships of AUS.