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A novel acetyl xylan esterase enabling complete deacetylation of substituted xylans
- Razeq, Fakhria M., Jurak, Edita, Stogios, Peter J., Yan, Ruoyu, Tenkanen, Maija, Kabel, Mirjam A., Wang, Weijun, Master, Emma R.
- Biotechnology for biofuels 2018 v.11 no.1 pp. 74
- enzyme activity, esterases, hardwood, loci, moieties, xylan
- BACKGROUND: Acetylated 4-O-(methyl)glucuronoxylan (GX) is the main hemicellulose in deciduous hardwood, and comprises a β-(1→4)-linked xylopyranosyl (Xylp) backbone substituted by both acetyl groups and α-(1→2)-linked 4-O-methylglucopyranosyluronic acid (MeGlcpA). Whereas enzymes that target singly acetylated Xylp or doubly 2,3-O-acetyl-Xylp have been well characterized, those targeting (2-O-MeGlcpA)3-O-acetyl-Xylp structures in glucuronoxylan have remained elusive. RESULTS: An unclassified carbohydrate esterase (FjoAcXE) was identified as a protein of unknown function from a polysaccharide utilization locus (PUL) otherwise comprising carbohydrate-active enzyme families known to target xylan. FjoAcXE was shown to efficiently release acetyl groups from internal (2-O-MeGlcpA)3-O-acetyl-Xylp structures, an activity that has been sought after but lacking in known carbohydrate esterases. FjoAcXE action boosted the activity of α-glucuronidases from families GH67 and GH115 by five and nine times, respectively. Moreover, FjoAcXE activity was not only restricted to GX, but also deacetylated (3-O-Araf)2-O-acetyl-Xylp of feruloylated xylooligomers, confirming the broad substrate range of this new carbohydrate esterase. CONCLUSION: This study reports the discovery and characterization of the novel carbohydrate esterase, FjoAcXE. In addition to cleaving singly acetylated Xylp, and doubly 2,3-O-acetyl-Xylp, FjoAcXE efficiently cleaves internal 3-O-acetyl-Xylp linkages in (2-O-MeGlcpA)3-O-acetyl-Xylp residues along with densely substituted and branched xylooligomers; activities that until now were missing from the arsenal of enzymes required for xylan conversion.