Effects of Site-directed Mutagenesis on the Catalytic Activity of Caffeine Synthase Gene (YH-NMT1) Involved in Caffeine Synthesis in Camellia Sinensis
Caffeine is an important functional substance in Camellia sinensis, and can be synthesized by complex biosynthesis pathways, including the major pathway and by-pass pathway.The major biosynthesis pathway is xanthosine→7-methylxanthosine→7-methylxanthine→theobromine→caffeine with three N-methyl transfer reactions and a nucleosidase reaction.The by-pass pathway mainly contains 7-methylxanthine→1,7-dimethylxanthine→caffeine, 3-methylxanthine→theobromine→caffeine and 3-methylxanthine→ 1,3-methylxanthine→caffeine.N-methyltransferase (NMT), which is a S-(5-Adenosyl)-L-methionine(SAM)-dependent enzyme, play an important role in the regulation of N-methyl transfer reactions during the progress of the caffeine biosynthesis.Several reported NMT genes such as TCS1(AB031280), ICS1(AB056108) and PCS1(AB207817) had been cloned from Camellia sinensis.In this study, a new gene YH-NMT1 was screened from the cDNA library of Yinghong 9.It shared more than 80％ homology in amino acid sequence compared with the cloned genes, but had complex enzyme activity including catalyzing 3-methylxanth to 1,3-dimethylxanthine (theophylline), 7-methylxanthine to 3,7-dimethylxanthine (theobromine),1,7-dimethylxanthine to 1,3,7-trimethylxanthine (caffeine), and 3,7-dimethylxanthine to 1,3,7-trimethylxanthine (caffeine).Therefore, it is very interesting to figure out the substrate specificity and catalytic activity related to YH-NMT1.
CHEN Xiao-fang YAN Chang-yu REN Qiu-jing XU Yu-hua JIAO Yi LI Bin CHEN Zhong-zheng
College of Food Science, South China Agricultural University, Guangzhou, 510642, China
国际会议
International Tea Symposium 2014(ITS 2014)(国际茶叶学术研讨会)
杭州
英文
214-216
2014-09-10（万方平台首次上网日期，不代表论文的发表时间）