Selective chemical depolymerization of rhamnogalacturonans.
A method was developed to selectively methyl esterify and then cleave GalA residues in pectic polysaccharides. The method was optimized using a rhamnogalacturonan (RG) from Arabidopsis mucilage as a model compound. The carboxyl group of the GalA residues in the RG was selectively methyl esterified using tetrabutylammonium fluoride and iodomethane in Me(2)SO containing 8% water. A 1D HMQC NMR method to determine the degree of methyl esterification was developed using (13)C-iodomethane as the methylating agent. The methyl-esterified pectins were fragmented by beta-elimination in 0.2M sodium borate, pH7.3, at 125 degrees C. The resulting oligoglycosyl fragments, which contain a nonreducing 4-deoxy-beta-l-threo-hex-4-enepyranosyluronic acid residue, were characterized using MALDI-TOF mass spectrometry, monosaccharide composition analysis, and 1D and 2D (1)H and (13)C NMR spectroscopy. Application of this method to branched RG from potato generated low-molecular-weight fragments containing two residues from the RG backbone and a single side chain. In contrast, the fragments obtained when RG is treated with RG lyase contain a minimum of four backbone residues. The chemical method thus facilitates the release and structural characterization of the side-chain structures of RG obtained from various plant sources. The method also provides a convenient method for generating fully or partially methyl-esterified homogalacturonans.
Deng
Chenghua
C
Complex Carbohydrate Research Center, The University of Georgia, 315 Riverbend Road, Athens, GA 30602-4712, USA.
O'Neill
Malcolm A
MA
York
William S
WS
D017360:Arabidopsis / Q000737:chemistry; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D004951:Esterification; D006603:Hexuronic Acids / Q000737:chemistry; D008969:Molecular Sequence Data; D010368:Pectins / Q000737:chemistry* / Q000378:metabolism; D011108:Polymers / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D006603:Hexuronic Acids; D011108:Polymers; C007819:galacturonic acid; D010368:Pectins; C003181:polygalacturonic acid