title: The two Rasamsonia emersonii α-glucuronidases, ReGH67 and ReGH115, show a different mode-of-action towards glucuronoxylan and glucuronoxylo-oligosaccharides.
abstract: BACKGROUND
  The production of biofuels and biochemicals from grass-type plant biomass requires a complete utilisation of the plant cellulose and hemicellulosic xylan via enzymatic degradation to their constituent monosaccharides. Generally, physical and/or thermochemical pretreatments are performed to enable access for the subsequent added carbohydrate-degrading enzymes. Nevertheless, partly substituted xylan structures remain after pretreatment, in particular the ones substituted with (4-O-methyl-)glucuronic acids (UAme). Hence, α-glucuronidases play an important role in the degradation of UAmexylan structures facilitating the complete utilisation of plant biomass. The characterisation of α-glucuronidases is a necessity to find the right enzymes to improve degradation of recalcitrant UAmexylan structures.
  
  
  RESULTS
  The mode-of-action of two α-glucuronidases was demonstrated, both obtained from the fungus Rasamsonia emersonii; one belonging to the glycoside hydrolase (GH) family 67 (ReGH67) and the other to GH115 (ReGH115). Both enzymes functioned optimal at around pH 4 and 70 °C. ReGH67 was able to release UAme from UAme-substituted xylo-oligosaccharides (UAmeXOS), but only the UAme linked to the non-reducing end xylosyl residue was cleaved. In particular, in a mixture of oligosaccharides, UAmeXOS having a degree of polymerisation (DP) of two were hydrolysed to a further extent than longer UAmeXOS (DP 3-4). On the contrary, ReGH115 was able to release UAme from both polymeric UAmexylan and UAmeXOS. ReGH115 cleaved UAme from both internal and non-reducing end xylosyl residues, with the exception of UAme attached to the non-reducing end of a xylotriose oligosaccharide.
  
  
  CONCLUSIONS
  In this research, and for the first time, we define the mode-of-action of two α-glucuronidases from two different GH families both from the ascomycete R. emersonii. To date, only four α-glucuronidases classified in GH115 are characterised. ReGH67 showed limited substrate specificity towards only UAmeXOS, cleaving UAme only when attached to the non-reducing end xylosyl residue. ReGH115 was much less substrate specific compared to ReGH67, because UAme was released from both polymeric UAmexylan and UAmeXOS, from both internal and non-reducing end xylosyl residues. The characterisation of the mode-of-action of these two α-glucuronidases helps understand how R. emersonii attacks UAmexylan in plant biomass and the knowledge presented is valuable to improve enzyme cocktails for biorefinery applications.
authors.affiliation: Laboratory of Food Chemistry, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands.
authors.forename: Patricia Murciano
authors.initials: PM
authors.lastname: Martínez
authors.affiliation: DSM Biotechnology Center, Alexander Fleminglaan 1, 2613 AX Delft, The Netherlands.
authors.forename: Maaike M
authors.initials: MM
authors.lastname: Appeldoorn
authors.affiliation: Laboratory of Food Chemistry, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands.
authors.forename: Harry
authors.initials: H
authors.lastname: Gruppen
authors.affiliation: Laboratory of Food Chemistry, Wageningen University, Bornse Weilanden 9, 6708 WG Wageningen, The Netherlands.
authors.forename: Mirjam A
authors.initials: MA
authors.lastname: Kabel
keywords: Biorefinery; GH115; GH67; Rasamsonia emersonii; Xylo-oligosaccharides; α-Glucuronidase