Structural basis for acceptor-substrate recognition of UDP-glucose: anthocyanidin 3--glucosyltransferase from

Hiromoto, Takeshi; Honjo, Eijiro*; Tamada, Taro; Kuroki, Ryota; Noda, Hisanobu*; Kazuma, Kohei*; Suzuki, Masahiko*

UDP-glucose: anthocyanidin 3--glucosyltransferase from (3GT-A) catalyzes the transfer of glucose from UDP-glucose to anthocyanidins such as delphinidin. The glucosylation of delphinidin at the 3-hydroxyl group has been proposed as an initial glucosylation step toward the biosynthesis of ternatins, which are blue anthocyanins found in the petals of . Although the crystal structures of several flavonoid glycosyltransferases (UGTs) were determined, the acceptor-substrate complexes were limited to the flavonol-bound forms. Here, in order to understand the acceptor-recognition scheme of 3GT-A, the crystal structures in complex with anthocyanidin delphinidin and petunidin, and flavonol kaempferol were determined to resolutions of 2.6 , 2.7 , and 1.8 respectively. The enzyme recognition of unstable anthocyanidins was firstly observed in this structural determination; nevertheless, the molecular orientations of these three acceptors in the binding site are different from those of the known flavonoid UGTs, GT1 and UGT78G1. The crystal structures of 3GT-A provide insight not only into anthocyanidin configurations in enzyme, but also into a different binding scheme for acceptor-substrate recognition compared with the known UGTs.