Arabidopsis AtCYP71B23: Detection of non-CYP74 enzyme of oxylipin biosynthesis

The CYP71 clan comprises the majority of Arabidopsis thaliana P450s. The functional role of the great majority of CYP71 clan enzymes remains unknown hitherto. Some Arabidopsis CYP71B subfamily proteins, such as AtCYP71B23, exhibit primary structural similarities to CYP74 enzymes and prostacyclin synthase (CYP8A1). Particularly, AtCYP71B23 and some related CYP71B proteins, along with the CYP74s and CYP8A1, exhibit a critical substitution of the D/E residue, which is conserved in monooxygenases, in the centre of the I-helix groove motif, with an asparagine (N) residue. This substitution may result in a nonclassical behaviour of these P450s. These observations prompted us to prepare the recombinant AtCYP71B23 and examine its behaviour towards the fatty acid hydroperoxides. AtCYP71B23 was active towards the linoleic acid 9(S)-hydroperoxides of linoleic (9-HPOD) and α-linolenic (9-HPOT) acids, as well as the 13(S)-hydroperoxide of linoleic acid (13-HPOD). α-Linolenic acid 13(S)-hydroperoxide was an inefficient substrate. Major products were the divinyl ethers (1'Z)-colneleic (9-HPOD), (1'Z)-colnelenic (9-HPOT), and (11Z)-etheroleic (13-HPOD) acids. Thus, AtCYP71B23 is an unprecedented CYP71 clan enzyme of fatty acid hydroperoxide metabolism and behaves primarily as a divinyl ether synthase.