An enzyme activity capable of endotransglycosylation of heteroxylan polysaccharides is present in plant primary cell walls

Abstract

Heteroxylans in the plant cell wall have been proposed to have a role analogous to that of xyloglucans or heteromannans, forming growth-restraining networks by interlocking cellulose microfibrils. A xylan endotransglycosylase has been identified that can transglycosylate heteroxylan polysaccharides in the presence of xylan-derived oligosaccharides. High activity was detected in ripe fruit of papaya (Carica papaya), but activity was also found in a range of other fruits, imbibed seeds and rapidly growing seedlings of cereals. Xylan endotransglycosylase from ripe papaya fruit used a range of heteroxylans, such as wheat arabinoxylan, birchwood glucuronoxylan and various heteroxylans from dicotyledonous primary cell walls purified from tomato and papaya fruit, as donor molecules. As acceptor molecules, the enzyme preferentially used xylopentaitol over xylohexaitol or shorter-length acceptors. Xylan endotransglycosylase was active over a broad pH range and could perform transglycosylation reactions up to 55 °C. Xylan endotransglycosylase activity was purified from ripe papaya fruit by ultrafiltration and cation exchange chromatography. Highest endotransglycosylase activity was identified in fractions that also contained high xylan hydrolase activity and correlated with the presence of the endoxylanase CpaEXY1. Recombinant CpaEXY1 protein transiently over-expressed in Nicotiana benthamiana leaves showed both endoxylanase and xylan endotransglycosylase activities in vitro, suggesting that CpaEXY1 is a single enzyme with dual activity in planta. Purified native CpaEXY1 showed two- to fourfold higher endoxylanase than endotransglycosylase activity, suggesting that CpaEXY1 may act primarily as a hydrolase. We propose that xylan endotransglycosylase activity (like xyloglucan and mannan endotransglycosylase activities) could be involved in remodelling or re-arrangement of heteroxylans of the cellulose-non-cellulosic cell wall framework.

Identification and enzymatic characterization of an endo-1,3-β-glucanase from Euglena gracilis

“…knowledge, EgCel17A is the first heat-stable endo-1,3-b-glucanase found in algae. By contrast, exo-glucanses (b-glucosidase, b-mannosidase and galactosidase) and endotransglucosylases for xyloglucan, b-1,4-glucan and xylan have been reported to catalyze transglycosylation reaction (Nishitani and Tominaga, 1992;Fry et al, 1992;Shi et al, 2011;Gupta et al, 2012;Bhatia et al, 2002;Ducret et al, 2002;Johnstone et al, 2013;Takahashi et al, 2013), EgCel17A catalyzed hydrolysis and transglycosylation of b-1,3-glucan (Fig. 4).…”

Genetics of Fruit Softening

“…deliciosa and A. eriantha (Schröder et al 2004). Xylan endotransglycosylase activity has been reported in ripe avocado, banana, pineapple and apple, but not as yet in kiwifruit (Johnston et al 2013). …”

“…Each enzyme potentially possesses two enzymatic activities, a hydrolase activity (XEH, MEH, XyEH) (Fanutti et al 1993;Bewley et al 2000;Chen and Paull 2003) and/or a transglycosylase activity (XET, MET, XyET) (Schröder et al 1998Rose et al 2002;Johnston et al 2013). The hydrolase activity leads to the depolymerisation of the target hemicellulose.…”

Microorganisms for Biorefining of Green Biomass

“…The fresh green juice containing high-value protein, phytochemicals and easily accessible carbohydrates is used for direct lactic acid fermentation, which eliminates some of the challenges associated with pretreatment processes and heat sterilisation such as inhibitor formation and high energy usage (Kamm and Kamm 2004;Kerfai et al 2011). Another advantage of using fresh biomass in the green biorefinery is that the natural enzymes in the juice are still active after cropping, helping the release of fermentable sugars (Johnston et al 2013;Dodić et al 2009). …”