Abstract
Xylanases are the enzymes that catalyze the breakdown of the main hemicellulose present in plant cell walls. They have attracted attention due to their biotechnological potential for the preparation of industrially interesting products from lignocellulose. While many xylanases have been characterized from bacteria and filamentous fungi, information on yeast xylanases is scarce and no yeast xylanase belonging to glycoside hydrolase (GH) family 30 has been described so far. Here, we cloned, expressed and characterized GH30 xylanase SlXyn30A from the yeast Sugiyamaella lignohabitans. The enzyme is active on glucuronoxylan (8.4 U/mg) and rhodymenan (linear β-1,4-1,3-xylan) (3.1 U/mg) while its activity on arabinoxylan is very low (0.03 U/mg). From glucuronoxylan SlXyn30A releases a series of acidic xylooligosaccharides of general formula MeGlcA2Xyln. These products, which are typical for GH30-specific glucuronoxylanases, are subsequently shortened at the non-reducing end, from which xylobiose moieties are liberated. Xylobiohydrolase activity was also observed during the hydrolysis of various xylooligosaccharides. SlXyn30A thus expands the group of glucuronoxylanases/xylobiohydrolases which has been hitherto represented only by several fungal GH30-7 members.
Highlights
Endo-β-1,4-xylanases (EXs, EC 3.2.1.8) are main xylan depolymerizing enzymes cleaving the polysaccharide backbone to xylooligosaccharides (XOs) of various lengths
GH30 enzymes, SlXyn30A showed the highest similarity (65.9%) and identity (47.7%) to xylanase C from Talaromyces purpureogenus, but other hits showed a similar level of homology and identity: glucuronoxylanase/xylobiohydrolase TtXyn30A from Thermothelomyces thermophila (65.5% similarity, 47.5% identity), glucuronoxylanase/xylobiohydrolase TcXyn30B
Asn90 in this loop corresponds to Asn93 in TcXyn3B and Asp78 in TtXyn30A which are supposed to play a role in xylobiohydrolase activity of the GH30-7 glucuronoxylanases [4,9]
Summary
Endo-β-1,4-xylanases (EXs, EC 3.2.1.8) are main xylan depolymerizing enzymes cleaving the polysaccharide backbone to xylooligosaccharides (XOs) of various lengths. Prokaryotic EXs are grouped into subfamily GH30-8, while eukaryotic xylanases are members of GH30-7 subfamily. Catalytic properties of the GH30-8 subfamily enzymes are quite uniform and most of them are specific glucuronoxylanases (EC 3.2.1.136) requiring glucuronic or 4-O-methyl-glucuronic acid (MeGlcA) substitution of the main chain for their action [13,14,15]. Catalytic properties of the GH30-7 subfamily representatives are diverse and include specific glucuronoxylanases, xylobiohydrolases, non-specific endoxylanases, endoxylanases/xylobiohydrolases and xylanases releasing xylose from the reducing end of the substrate [11,12]. All characterized GH30-7 xylanases come from filamentous fungi and so far no yeast GH30 EX has been described
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