title: Effects of enzymatic removal of plant cell wall acylation (acetylation, p-coumaroylation, and feruloylation) on accessibility of cellulose and xylan in natural (non-pretreated) sugar cane fractions.
abstract: BACKGROUND
  Sugar cane internodes can be divided diagonally into four fractions, of which the two innermost ones are the least recalcitrant pith and the moderately accessible pith-rind interface. These fractions differ in enzymatic hydrolyzability due to structural differences. In general, cellulose hydrolysis in plants is hindered by its physical interaction with hemicellulose and lignin. Lignin is believed to be linked covalently to hemicellulose through hydroxycinnamic acids, forming a compact matrix around the polysaccharides. Acetyl xylan esterase and three feruloyl esterases were evaluated for their potential to fragment the lignocellulosic network in sugar cane and to indirectly increase the accessibility of cellulose.
  
  
  RESULTS
  The hydrolyzability of the pith and pith-rind interface fractions of a low-lignin-containing sugar cane clone (H58) was compared to that of a reference cultivar (RC). Acetyl xylan esterase enhanced the rate and overall yield of cellulose and xylan hydrolysis in all four substrates. Of the three feruloyl esterases tested, only TsFaeC was capable of releasing p-coumaric acid, while AnFaeA and NcFaeD released ferulic acid from both the pith and interface fractions. Ferulic acid release was higher from the less recalcitrant clone (H58)/fraction (pith), whereas more p-coumaric acid was released from the clone (RC)/fraction (interface) with a higher lignin content. In addition, a compositional analysis of the four fractions revealed that p-coumaroyl content correlated with lignin, while feruloyl content correlated with arabinose content, suggesting different esterification patterns of these two hydroxycinnamic acids. Despite the extensive release of phenolic acids, feruloyl esterases only moderately promoted enzyme access to cellulose or xylan.
  
  
  CONCLUSIONS
  Acetyl xylan esterase TrAXE was more efficient in enhancing the overall saccharification of sugar cane, compared to the feruloyl esterases AnFaeA, TsFaeC, and NcFaeD. The hydroxycinnamic acid composition of sugar cane fractions and the hydrolysis data together suggest that feruloyl groups are more likely to decorate xylan, while p-coumaroyl groups are rather linked to lignin. The three different feruloyl esterases had distinct product profiles on non-pretreated sugar cane substrate, indicating that sugar cane pith could function as a possible natural substrate for feruloyl esterase activity measurements. Hydrolysis data suggest that TsFaeC was able to release p-coumaroyl groups esterifying lignin.
authors.affiliation: Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O. Box 5003, N-1432, Aas, Norway ; VTT Technical Research Centre of Finland, P.O. Box 1000, Espoo, 02044 VTT Finland ; Department of Food and Environmental Sciences, University of Helsinki, P.O. Box 27, Helsinki, 00014 Finland.
authors.forename: Anikó
authors.initials: A
authors.lastname: Várnai
authors.affiliation: Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de São Paulo, 12602-810 Lorena, SP Brasil.
authors.forename: Thales Hf
authors.initials: TH
authors.lastname: Costa
authors.affiliation: INRA, UMR 1163 Biodiversité et Biotechnologie Fongiques (BBF), POLYTECH, Aix Marseille Université, 163 avenue de Luminy, 13288 Marseille, Cedex 09 France ; Aix-Marseille Université, INRA, BBF UMR_A 1163, 163 avenue de Luminy, 13288 Marseille, cedex 09 France.
authors.forename: Craig B
authors.initials: CB
authors.lastname: Faulds
authors.affiliation: Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de São Paulo, 12602-810 Lorena, SP Brasil.
authors.forename: Adriane Mf
authors.initials: AM
authors.lastname: Milagres
authors.affiliation: VTT Technical Research Centre of Finland, P.O. Box 1000, Espoo, 02044 VTT Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Siika-Aho
authors.affiliation: Departamento de Biotecnologia, Escola de Engenharia de Lorena, Universidade de São Paulo, 12602-810 Lorena, SP Brasil.
authors.forename: André
authors.initials: A
authors.lastname: Ferraz
keywords: Acetyl xylan esterase (AXE); Feruloyl esterase (FAE); Hydrolysis; Lignin; Sugar cane