Abstract:l‐Galactose (l‐Gal) is one of the components of plant cell wall polysaccharides. In the GDP‐l‐fucose‐deficient Arabidopsis thaliana mutant mur1, l‐fucose (l‐Fuc) residues in xyloglucan are substituted by l‐Gal residues. l‐Gal only differs from l‐Fuc by the presence of an oxygen at C‐6. Thus, we hypothesized that the A. thaliana xyloglucan α1,2‐l‐fucosyltransferase (AtFUT1) is also responsible for the l‐galactosyl transfer to d‐galactose residues in xyloglucan. In this study, we heterologously produced AtFUT1 i… Show more
“…Supporting this idea, the same phenomenon has been observed in the unrelated GT61 family (Cenci et al ., 2018 ; Zhong et al ., 2022 ). Generally, many glycosyltransferases exhibit some level of donor substrate promiscuity (Laursen et al ., 2018 ; Ohashi et al ., 2018 ; Biswas & Thattai, 2020 ; Ehrlich et al ., 2021 ), so the effective activity could depend to some extent on the availability of the relevant sugar nucleotides. Interestingly, however, and in contrast to glycosyl hydrolases, there is not yet any evidence for Ara f /Xyl promiscuity in any member of the GT47 or GT61 families.…”
Summary
Xyloglucan is an abundant polysaccharide in many primary cell walls and in the human diet. Decoration of its α‐xylosyl sidechains with further sugars is critical for plant growth, even though the sugars themselves vary considerably between species. Plants in the Ericales order – prevalent in human diets – exhibit β1,2‐linked xylosyl decorations. The biosynthetic enzymes responsible for adding these xylosyl decorations, as well as the hydrolases that remove them in the human gut, are unidentified.
GT47 xyloglucan glycosyltransferase candidates were expressed in Arabidopsis and endo‐xyloglucanase products from transgenic wall material were analysed by electrophoresis, mass spectrometry, and nuclear magnetic resonance (NMR) spectroscopy. The activities of gut bacterial hydrolases BoGH43A and BoGH43B on synthetic glycosides and xyloglucan oligosaccharides were measured by colorimetry and electrophoresis.
CcXBT1 is a xyloglucan β‐xylosyltransferase from coffee that can modify Arabidopsis xyloglucan and restore the growth of galactosyltransferase mutants. Related VmXST1 is a weakly active xyloglucan α‐arabinofuranosyltransferase from cranberry. BoGH43A hydrolyses both α‐arabinofuranosylated and β‐xylosylated oligosaccharides.
CcXBT1's presence in coffee and BoGH43A's promiscuity suggest that β‐xylosylated xyloglucan is not only more widespread than thought, but might also nourish beneficial gut bacteria. The evolutionary instability of transferase specificity and lack of hydrolase specificity hint that, to enzymes, xylosides and arabinofuranosides are closely resemblant.
“…Supporting this idea, the same phenomenon has been observed in the unrelated GT61 family (Cenci et al ., 2018 ; Zhong et al ., 2022 ). Generally, many glycosyltransferases exhibit some level of donor substrate promiscuity (Laursen et al ., 2018 ; Ohashi et al ., 2018 ; Biswas & Thattai, 2020 ; Ehrlich et al ., 2021 ), so the effective activity could depend to some extent on the availability of the relevant sugar nucleotides. Interestingly, however, and in contrast to glycosyl hydrolases, there is not yet any evidence for Ara f /Xyl promiscuity in any member of the GT47 or GT61 families.…”
Summary
Xyloglucan is an abundant polysaccharide in many primary cell walls and in the human diet. Decoration of its α‐xylosyl sidechains with further sugars is critical for plant growth, even though the sugars themselves vary considerably between species. Plants in the Ericales order – prevalent in human diets – exhibit β1,2‐linked xylosyl decorations. The biosynthetic enzymes responsible for adding these xylosyl decorations, as well as the hydrolases that remove them in the human gut, are unidentified.
GT47 xyloglucan glycosyltransferase candidates were expressed in Arabidopsis and endo‐xyloglucanase products from transgenic wall material were analysed by electrophoresis, mass spectrometry, and nuclear magnetic resonance (NMR) spectroscopy. The activities of gut bacterial hydrolases BoGH43A and BoGH43B on synthetic glycosides and xyloglucan oligosaccharides were measured by colorimetry and electrophoresis.
CcXBT1 is a xyloglucan β‐xylosyltransferase from coffee that can modify Arabidopsis xyloglucan and restore the growth of galactosyltransferase mutants. Related VmXST1 is a weakly active xyloglucan α‐arabinofuranosyltransferase from cranberry. BoGH43A hydrolyses both α‐arabinofuranosylated and β‐xylosylated oligosaccharides.
CcXBT1's presence in coffee and BoGH43A's promiscuity suggest that β‐xylosylated xyloglucan is not only more widespread than thought, but might also nourish beneficial gut bacteria. The evolutionary instability of transferase specificity and lack of hydrolase specificity hint that, to enzymes, xylosides and arabinofuranosides are closely resemblant.
“…The remaining Os FUTs may fucosylate other cell wall polymers but have broad acceptor substrates in vitro and thus show activity on TXyG. It is not known if these Os FUTs use GDP- l -Gal as well as GDP-Fuc as donor substrates, as has been demonstrated for At FUT1 ( 46 ). Figure 6 Fucosyltransferase activity of 15 putative rice Os FUTs members of the GT37 family on i -GT-ray platform .…”
“…The promiscuous nature of FucT has also been observed in vivo in the l -fucose deficient mur1 mutant of A. thaliana ( Zablackis et al, 1996 ), in which l -galactose replaces the absent l -fucose as a required component of the biologically active cell wall xyloglucan-derived oligosaccharides. l -Galactosylation of these xyloglucan oligosaccharides by At FucT has recently also been demonstrated in vitro ( Ohashi et al, 2019 ). In vivo , the GDP- l -Gal is most likely obtained via de novo synthesis over GDP-Man and thus utilizing the GM35E.…”
GDP-mannose 3,5-epimerase (GM35E, GME) belongs to the short-chain dehydrogenase/reductase (SDR) protein superfamily and catalyses the conversion of GDP-d-mannose towards GDP-l-galactose. Although the overall reaction seems relatively simple (a double epimerization), the enzyme needs to orchestrate a complex set of chemical reactions, with no less than 6 catalysis steps (oxidation, 2x deprotonation, 2x protonation and reduction), to perform the double epimerization of GDP-mannose to GDP-l-galactose. The enzyme is involved in the biosynthesis of vitamin C in plants and lipopolysaccharide synthesis in bacteria. In this review, we provide a clear overview of these interesting epimerases, including the latest findings such as the recently characterized bacterial and thermostable GM35E representative and its mechanism revision but also focus on their industrial potential in rare sugar synthesis and glycorandomization.
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