2004 Fiscal Year Final Research Report Summary
Characterization of the metal binding site of rhamnogalacturonan II from plant cell walls
| Project/Area Number |
15580053
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Plant nutrition/Soil science
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| Research Institution | National Agriculture and Bio-oriented Research Organization |
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Principal Investigator |
MATSUNAGA Toshiro National Agricultural Research Center for Kyushu Okinawa Region, Chief, 生物系特定産業技術研究機構・九州沖縄農業研究センター, 研究室長 (20355647)
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| Project Period (FY) |
2003 – 2004
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| Keywords | rhamnogalacturonan II / lanthanoid / size-exclusion HPLC / ICP-MS / plant cell-wall polysaccharide / boron |
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| Research Abstract |
Rhamnogalacturonan II (RG-II) is a structurally complex pectic polysaccharide isolated from vascular plant cell walls, and is composed of a backbone of galacturonic acid (GalA) residues and four side chains of diverse glycosyl residues. Recently, a dimeric RG-II - borate complex (dRG-II-B) in which a borate-diol ester (1:2) cross-links two monomeric RG-II (mRG-II) was isolated from pectinase digests of plant cell walls. It has been shown that RG-II is covalently linked to homogalacturonan, a major component of pectin in plant cell walls, and that dRG-II-B formation contributes to stabilization of the cell walls. These studies have demonstrated that the primary function of boron, an essential microelement for plants, is to covalently cross-link wall pectin by dRG-II-B formation, and thereby to contribute to the strength and integrity of the cell walls. The dRG-II-B complex contains specific metals, such as Ca, Sr, Ba, and Pb. However, the function of metal ions bound to dRG-II-B has not
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been established. In the present study, the metal contents of RG-II and its partial hydrolysates that were treated with metal ions were determined by size-exclusion high-performance liquid chromatography / inductively coupled plasma mass spectrometry (SE-HPLC/ICP-MS) to understand the RG-II's affinity and binding site for metals.
The partially hydrolyzed mRG-II (sugar beet and red wine) was treated with La^<3+>, and then analyzed by SE-HPLC/RI and SE-HPLC/ICP-MS to determine the contribution of each side chain of mRG-II to form a lanthanoid binding site. The amount and molecular weight of the mRG-II major peak gradually decreased with intensification of the hydrolysis treatment, which accompanied a decrease in the amount of La bound to the major peak. In the lower molecular weight region, no mRG-II fragment complexed with La was observed. These results indicate that the La binding site in mRG-II can be attributed not to a single glycosyl residue and side chain, but to an assembly of side chains and a GalA backbone. Less
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