セロビオース2-エピメラーゼ(CE)は,β-(1→4)-二糖の還元末端Glc残基をMan残基にエピメリ化する.β-マンナンの代謝においてManβ-4ManからManβ-4Glcを生成し,加リン酸分解へと導くとされる.CEの利用によるラクトースからのエピラクトースの生産技術が整備され,エピラクトースにプレバイオティクス効果など有益な生理機能が見出された.CEの構造は,触媒部位も含めてアシルグルコサミン2-エピメラーゼ(AGE)やマンノースイソメラーゼ(MI)などと類似し,AGEスーパーファミリーを形成する.(α/α)6バレルからなる触媒ドメインの8番目と12番目のα-ヘリックス上のHisが一般酸・塩基触媒として基質の2-Hの授受に働くcis-エンジオレート中間体を経由したエピメリ化機構が提唱された.一方,MIなどイソメラーゼでは,8番目のα-ヘリックス上のHisが一般酸・塩基触媒として基質の1-Cと2-Cの間でのプロトンの分子内転移を行う機構が考えられた.AGEスーパーファミリーからManをエピメリ化するマンノース2-エピメラーゼが発見され,GlcからのManの生産への応用が期待された.
Plants are sessile organisms and are unable to avoid environmental stresses by changing their habitats. Therefore, plants have developed unique and sophisticated responding systems. It has been generally accepted that plant use plant hormones to give actions toward (against) environmental changes and stress. Among of the hormones, jasmonic acid(s) has pivotal roles to perform the responses. In recent years, not only the activation of JA pathway but also the deactivations of active form JA are being paid a lot of attentions such as oxidations and glucosylations.
In previous our paper [1], we reported that Os SGT, putative salicylic acid glucosyltransferase, transferred glucosyl moiety toward 12-OHJA to afford 12-OGlcJA, and its mRNA was induced by wounding stress and JA and SA treatments. In the course of that study, we also found UDP-Glc independent glucosyl transferase activity to give preferably 12-OGlcJA in the crude extract of rice cell culture using octyl glucoside as donor molecule for supplying glucosyl moiety. There are few reports of the finding on UDP-Glc independent glucosyltransferase protein, and to our best knowledge, a report has been published by Matsuba et al. [2]. In this presentation we discuss elucidation of UDP-Glc independent glucosyl transferase toward 12-OHJA and 12-OHJA-Ile
[1] Seto Y. et al., Phytochemistry, 70, 370-379 (2009).
[2] Matsuba Y. et al.,Plant Cell,22, 3374-3389 (2010).