Uehara Yohei, Tamura Shunsuke, Maki Yusuke, Yagyu Kenta, Mizoguchi Tadashi, Tamiaki Hitoshi, Imai Tomoya, Ishii Tadashi, Ohashi Takao, Fujiyama Kazuhito, Ishimizu Takeshi
College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
College of Life Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan; Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
Biochem Biophys Res Commun. 2017 Apr 22;486(1):130-136. doi: 10.1016/j.bbrc.2017.03.012. Epub 2017 Mar 8.
The pectin in plant cell walls consists of three domains: homogalacturonan, rhamnogalacturonan (RG)-I, and RG-II. It is predicted that around 50 different glycosyltransferases are required for their biosynthesis. Among these, the activities of only a few glycosyltransferases have been detected because pectic oligosaccharides are not readily available for use as substrates. In this study, fluorogenic pyridylaminated RG-I-backbone oligosaccharides (PA-RGs) with 3-14 degrees of polymerization (DP) were prepared. Using these oligosaccharides, the activity of RG-I:rhamnosyltransferase (RRT), involved in the biosynthesis of the RG-I backbone diglycosyl repeating units (-4GalUAα1-2Rhaα1-), was detected from the microsomes of azuki bean epicotyls. RRT was found to prefer longer acceptor substrates, PA-RGs with a DP > 7, and it does not require any metal ions for its activity. RRT is located in the Golgi and endoplasmic reticulum. The activity of RRT coincided with epicotyl growth, suggesting that RG-I biosynthesis is involved in plant growth.
同型半乳糖醛酸聚糖、鼠李糖半乳糖醛酸聚糖（RG）-I和RG-II。据预测，其生物合成大约需要50种不同的糖基转移酶。其中，由于果胶寡糖不易用作底物，仅检测到少数几种糖基转移酶的活性。在本研究中，制备了聚合度（DP）为3至14的荧光吡啶胺化RG-I主链寡糖（PA-RGs）。利用这些寡糖，从赤豆胚轴的微粒体中检测到了参与RG-I主链二糖基重复单元（-4GalUAα1-2Rhaα1-）生物合成的RG-I：鼠李糖基转移酶（RRT）的活性。发现RRT更喜欢较长的受体底物，即DP>7的PA-RGs，并且其活性不需要任何金属离子。RRT位于高尔基体和内质网中。RRT的活性与胚轴生长一致，表明RG-I生物合成参与植物生长。
