Browse Articles

Article|09 Dec 2022|OPEN
Functional characterization and key residues engineering of a regiopromiscuity O-methyltransferase involved in benzylisoquinoline alkaloid biosynthesis in Nelumbo nucifera 
Yuetong Yu1 , Yan Liu1 , Gangqiang Dong2 , JinZhu Jiang1 , Liang Leng1 , XianJu Liu1 , Jun Zhang1 , An Liu1 , and Sha Chen,1 ,
1Key Laboratory of Beijing for Identification and Safety Evaluation of Chinese Medicine, Institute of Chinese Materia Medica, China Academy of Chinese Medical Sciences, No. 16, Nanxiaojie, Dongzhimennei, Beijing 100700, China
2Amway (China) Botanical R&D Centre, Wuxi 214115, China
*Corresponding author. E-mail: aliu@icmm.ac.cn,schen@icmm.ac.cn

Horticulture Research 10,
Article number: uhac276 (2023)
doi: https://doi.org/10.1093/hr/uhac276
Views: 260

Received: 23 Sep 2022
Accepted: 02 Dec 2022
Published online: 09 Dec 2022

Abstract

Lotus (Nelumbo nucifera), an ancient aquatic plant, possesses a unique pharmacological activity that is primarily contributed by benzylisoquinoline alkaloids (BIAs). However, only few genes and enzymes involved in BIA biosynthesis in N. nucifera have been isolated and characterized. In the present study we identified the regiopromiscuity of an O-methyltransferase, designated NnOMT6, isolated from N. nucifera; NnOMT6 was found to catalyze the methylation of monobenzylisoquinoline 6-O/7-O, aporphine skeleton 6-O, phenylpropanoid 3-O, and protoberberine 2-O. We further probed the key residues affecting NnOMT6 activity via molecular docking and molecular dynamics simulation. Verification using site-directed mutagenesis revealed that residues D316, N130, L135, N176A, D269, and E328 were critical for BIA O-methyltransferase activities; furthermore, N323A, a mutant of NnOMT6, demonstrated a substantial increase in catalytic efficiency for BIAs and a broader acceptor scope compared with wild-type NnOMT6. To the best of our knowledge, this is the first study to report the O-methyltransferase activity of an aporphine skeleton without benzyl moiety substitutions in N. nucifera. The study findings provide biocatalysts for the semisynthesis of related medical compounds and give insights into protein engineering to strengthen O-methyltransferase activity in plants.