title: Recovery and fine structure variability of RGII sub-domains in wine (Vitis vinifera Merlot).
abstract: OBJECTIVE
  Rhamnogalacturonan II (RGII) is a structurally complex pectic sub-domain composed of more than 12 different sugars and 20 different linkages distributed in five side chains along a homogalacturonan backbone. Although RGII has long been described as highly conserved over plant evolution, recent studies have revealed variations in the structure of the polysaccharide. This study examines the fine structure variability of RGII in wine, focusing on the side chains A and B obtained after sequential mild acid hydrolysis. Specifically, this study aims to differentiate intrinsic structural variations in these RGII side chains from structural variations due to acid hydrolysis.
  
  
  METHODS
  RGII from wine (Vitis vinifera Merlot) was sequentially hydrolysed with trifluoroacetic acid (TFA) and the hydrolysis products were separated by anion-exchange chromatography (AEC). AEC fractions or total hydrolysates were analysed by MALDI-TOF mass spectrometry.
  
  
  RESULTS
  The optimal conditions to recover non-degraded side chain B, side chain A and RGII backbone were 0·1 m TFA at 40 °C for 16 h, 0·48 m TFA at 40 °C for 16 h (or 0·1 m TFA at 60 °C for 8 h) and 0·1 m TFA at 60 °C for 16 h, respectively. Side chain B was particularly prone to acid degradation. Side chain A and the RGII GalA backbone were partly degraded by 0·1 m TFA at 80 °C for 1-4 h. AEC allowed separation of side chain B, methyl-esterified side chain A and non-methyl-esterified side chain A. The structure of side chain A and the GalA backbone were highly variable.
  
  
  CONCLUSIONS
  Several modifications to the RGII structure of wine were identified. The observed dearabinosylation and deacetylation were primarily the consequence of acidic treatment, while variation in methyl-esterification, methyl-ether linkages and oxidation reflect natural diversity. The physiological significance of this variability, however, remains to be determined.
authors.affiliation: INRA, UR1268 Biopolymères Interactions Assemblages, 44300 Nantes, France.
authors.forename: F
authors.initials: F
authors.lastname: Buffetto
authors.affiliation: INRA, UR1268 Biopolymères Interactions Assemblages, 44300 Nantes, France.
authors.forename: D
authors.initials: D
authors.lastname: Ropartz
authors.affiliation: Institute for Cell and Molecular Biosciences Medical School, Newcastle University, Framlington Place, UK.
authors.forename: X J
authors.initials: XJ
authors.lastname: Zhang
authors.affiliation: Institute for Cell and Molecular Biosciences Medical School, Newcastle University, Framlington Place, UK.
authors.forename: H J
authors.initials: HJ
authors.lastname: Gilbert
authors.affiliation: INRA, UR1268 Biopolymères Interactions Assemblages, 44300 Nantes, France.
authors.forename: F
authors.initials: F
authors.lastname: Guillon
authors.affiliation: INRA, UR1268 Biopolymères Interactions Assemblages, 44300 Nantes, France marie-christine.ralet@nantes.inra.fr.
authors.forename: M-C
authors.initials: MC
authors.lastname: Ralet
mesh_terms: D002473:Cell Wall / Q000737:chemistry* / Q000378:metabolism; D004951:Esterification; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D010368:Pectins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D027843:Vitis / Q000737:chemistry* / Q000378:metabolism; D014920:Wine
chemical_list: D011134:Polysaccharides; C042492:rhamnogalacturonan II; D010368:Pectins
keywords: MALDI-TOF; Merlot; Plant cell walls; RGII; Vitis vinifera; oligosaccharides; pectin; red wine; rhamnogalacturonan II