A novel bacterial GH30 xylobiohydrolase from Hungateiclostridium clariflavum

Typical bacterial GH30 xylanases are glucuronoxylanases requiring 4- O -methylglucuronic acid (MeGlcA) substitution of a xylan main chain for their action. They do not exhibit a significant activity on neutral xylooligosaccharides, arabinoxylan (AraX), or rhodymenan (Rho). In this work, the biochemical characterization of the bacterial Clocl_1795 xylanase from Hungateiclostridium (Clostridium) clariflavum DSM 19732 ( Hc Xyn30A) is presented. Amino acid sequence analysis of Hc Xyn30A revealed that the enzyme does not contain amino acids known to be responsible for MeGlcA coordination in the -2b subsite of glucuronoxylanases. This suggested that the catalytic properties of Hc Xyn30A may differ from those of glucuronoxylanases. Hc Xyn30A shows similar specific activity on glucuronoxylan (GX) and Rho, while the specific activity on AraX is about 1000 times lower. Hc Xyn30A releases Xyl 2 as the main product from the non-reducing end of different polymeric and oligomeric substrates. Catalytic properties of Hc Xyn30A resemble the properties of the fungal GH30 xylobiohydrolase from Acremonium alcalophilum , Aa Xyn30A. Hc Xyn30A is the first representative of a prokaryotic xylobiohydrolase. Its unique specificity broadens the catalytic diversity of bacterial GH30 xylanases. Key points • Bacterial GH30 xylobiohydrolase from H. clariflavum (HcXyn30A) has been characterized. • HcXyn30A releases xylobiose from the non-reducing end of different substrates. • HcXyn30A is the first representative of bacterial xylobiohydrolase.