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

BackgroundSugar 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.ResultsThe 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.ConclusionsAcetyl 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-014-0153-3) contains supplementary material, which is available to authorized users.

Phylogeny, classification and metagenomic bioprospecting of microbial acetyl xylan esterases

“…One of the areas where significant advances are possible is considered to be the exploitation of synergies derived from use of accessory enzymes (such as AcXEs) in conjunction with endo-acting cellulases and hemicellulases [2,29,45,107,[167][168][169]. Options for identification of novel (and possibly superior) variants of such enzymes include the use of new screening methodologies, and the targeting of under-explored biological communities.…”

Comparative evaluation of acid and alkaline sulfite pretreatments for enzymatic saccharification of bagasses from three different sugarcane hybrids

“…The conversion of sugarcane bagasse to platform sugars usually requires a pretreatment process due to the recalcitrant nature of lignocellulosic materials, making the carbohydrates more accessible to the hydrolytic enzymes . Previous studies have shown that the recalcitrance of sugarcane bagasse varies according to the characteristics of different sugarcane varieties (lignin contents, hemicellulose type, and structure) . However, other biomass characteristics such as size and volume of cell wall pores, accessible surface area, and cellulose crystallinity are also relevant factors on the enzymatic hydrolysis of cellulose …”

Ação do pré-tratamento com ácido sulfúrico diluído em híbridos de cana-de-açúcar e seus efeitos na conversão enzimática da glucana

“…Grohmann et al (1989) mostraram o efeito negativo dos grupos acetil da hemicelulose na hidrólise enzimática de palha de trigo e madeira (aspen), sendo menos pronunciado após 75 % de remoção; vale destacar que, para esses valores de remoção, através de solução de hidroxilamina, a conversão inicial de celulose aumentou em 2-3 vezes. Com uma abordagem biológica, um trabalho recente promoveu a remoção enzimática (acetil-esterase) dos grupos acetil de amostras de cana-de-açúcar, o que também possibilitou melhorar a taxa e o rendimento da hidrólise enzimática da celulose (VÁRNAI et al, 2014). A hemicelulose quando menos acetilada torna-se mais susceptível às enzimas presentes nos complexos enzimáticos, aumentando a acessibilidade da celulose e, posteriormente, os rendimentos de conversão (GROHMANN et al, 1989;VÁRNAI et al, 2014).…”

“…Com uma abordagem biológica, um trabalho recente promoveu a remoção enzimática (acetil-esterase) dos grupos acetil de amostras de cana-de-açúcar, o que também possibilitou melhorar a taxa e o rendimento da hidrólise enzimática da celulose (VÁRNAI et al, 2014). A hemicelulose quando menos acetilada torna-se mais susceptível às enzimas presentes nos complexos enzimáticos, aumentando a acessibilidade da celulose e, posteriormente, os rendimentos de conversão (GROHMANN et al, 1989;VÁRNAI et al, 2014).…”

“…No entanto, o real efeito da hemicelulose não pode ser facilmente isolado das demais transformações causadas pelo pré-tratamento, pois simultaneamente acontecem alterações na cristalinidade da celulose, na estrutura e na distribuição da lignina residual (JU; ENGELHARD; ZHANG, 2013). Os rendimentos de conversão enzimática da celulose podem ser aumentados com a remoção seletiva da hemicelulose, empregando xilanases (VÁRNAI et al, 2014); o que permite isolar o efeito desse componente estrutural e inferir sobre sua influência na intrínseca recalcitrância do material.…”