title: Mode of action of acetylxylan esterases on acetyl glucuronoxylan and acetylated oligosaccharides generated by a GH10 endoxylanase.
abstract: BACKGROUND
  Substitutions on the xylan main chain are widely accepted to limit plant cell wall degradability and acetylations are considered as one of the most important obstacles. Hence, understanding the modes of action of a range of acetylxylan esterases (AcXEs) is of ample importance not only to increase the understanding of the enzymology of plant decay/bioremediation but also to enable efficient bioconversion of plant biomass.
  
  
  METHODS
  In this study, the modes of action of acetylxylan esterases (AcXEs) belonging to carbohydrate esterase (CE) families 1, 4, 5 and 6 on xylooligosaccharides generated from hardwood acetyl glucuronoxylan were compared using MALDI ToF MS. Supporting data were obtained by following enzymatic deacetylation by (1)H NMR spectroscopy.
  
  
  CONCLUSIONS
  None of the used enzymes were capable of complete deacetylation, except from linear xylooligosaccharides which were completely deacetylated by some of the esterases in the presence of endoxylanase. A clear difference was observed between the performance of the serine-type esterases of CE families 1, 5 and 6, and the aspartate-metalloesterases of family CE4. The difference is mainly due to the inability of CE4 AcXEs to catalyze deacetylation of 2,3-di-O-acetylated xylopyranosyl residues. Complete deacetylation of a hardwood acetyl glucuronoxylan requires additional deacetylating enzyme(s).
  
  
  CONCLUSIONS
  The results contribute to the understanding of microbial degradation of plant biomass and outline the way to achieve complete saccharification of plant hemicelluloses which did not undergo alkaline pretreatment.
authors.affiliation: Institute of Chemistry, Center of Glycomics, Slovak Academy of Sciences, Dúbravská cesta 9, 84538 Bratislava, Slovakia. Electronic address: chempbsa@savba.sk.
authors.forename: Peter
authors.initials: P
authors.lastname: Biely
authors.forename: Mária
authors.initials: M
authors.lastname: Cziszárová
authors.forename: Iveta
authors.initials: I
authors.lastname: Uhliariková
authors.forename: Jane W
authors.initials: JW
authors.lastname: Agger
authors.forename: Xin-Liang
authors.initials: XL
authors.lastname: Li
authors.forename: Vincent G H
authors.initials: VG
authors.lastname: Eijsink
authors.forename: Bjorge
authors.initials: B
authors.lastname: Westereng
mesh_terms: D000107:Acetylation; D000115:Acetylesterase / Q000737:chemistry* / Q000378:metabolism; D018533:Biomass; D002240:Carbohydrate Sequence; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry* / Q000378:metabolism; D004950:Esterases / Q000737:chemistry / Q000378:metabolism; D005965:Glucuronates / Q000737:chemistry / Q000378:metabolism; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014990:Xylans / Q000737:chemistry / Q000378:metabolism
chemical_list: D005965:Glucuronates; D009844:Oligosaccharides; D010940:Plant Proteins; D011134:Polysaccharides; D014990:Xylans; C570991:xylooligosaccharide; C038910:glucuronoxylan; C007916:hemicellulose; D004950:Esterases; C022635:serine esterase; D000115:Acetylesterase; C081851:acetylxylan esterase; D043364:Endo-1,4-beta Xylanases
keywords: 4-O-methyl-d-glucuronic acid or 4-O-methyl-d-glucuronosyl; 4-O-methyl-d-glucuronosyl–α-1,2-d-xylopyranosyl–β-1,4-xylopyranosyl–β-1,4-xylopyranose (the upper index indicates the number of the xylosyl residues from the reducing end substituted with MeGlcA); AcXE; Acetyl glucuronoxylan; Acetylxylan esterase; CE; Carbohydrate esterase family; HexXyl(x)Ac(y); MALDI ToF MS; MeGlcA; MeGlcA(3)Xyl(3); MeGlcAXyl(x)Ac(y); NMR; Positional specificity; UXyl(x)Ac(y); Xyl(2)–Xyl(7); Xyl(x)Ac(y); Xylp; acetylated aldouronic acid containing one MeGlcA, x xylose residues and y acetyl groups; acetylated β-1,4-xylooligosaccharide containing x xylose residues and y acetyl groups; acetylxylan esterase; carbohydrate esterase; d-xylopyranose or d-xylopyranosyl; oligosaccharide containing an unknown component U, x xylose residues and y acetyl groups; oligosaccharide containing one hexopyranose residue of unknown nature, x xylose residues and y acetyl groups; β-1,4-xylobiose–β-1,4-xyloheptaose