Abstract
BackgroundThe strain Paenibacillus physcomitrellae XB isolated from moss of Physcomitrella patens was found have the xylan degradation ability, but its degradation characteristics and the related mechanism has not been revealed.ResultsIn this study, Paenibacillus physcomitrellae XB exhibited different xylan degradation ability under the different substrates of corncob xylan (CCX), oat spet xylan (OSX), wheat flour arabinoxylan (AX) and beech wood xylan (BWX). Genomic analysis showed that ~ 38 genes were related to xylan degradation, and quantitative real time RT-PCR showed that two glycoside hydrolase family 43 genes (Pph_0602 and Pph_2344) were up-regulated on 1% CCX and xylose. Substrate-specific experiments with purified proteins Ppxyl43A (Pph_0602) and Ppxyl43B (Pph_2344) revealed that both of them exhibited β-xylosidase activity toward chromogenic substrate p-nitrophenyl–D-xylopyranoside and α-L-arabinofuranosidase activity toward p-nitrophenyl-α-L-arabinofuranoside, indicating at least bifunctionality. Combined their degradation features on the natural substrates of different xylans with the hydrolytic products separated by thin-layer chromatography and high-performance anion exchange chromatography profiles, it was found that both Ppxyl43A and Ppxyl43B were with the similar degradation ability on xylo-oligosaccharides (like CCX, OSX, xylohexaose and xylobiose). Both of them even could hydrolyze xylohexaose and xylobiose completely to xylose, but could not hydrolyze BWX and AX to produce xylooligosaccharides or xylose, suggesting they have no endo-xylanase activity and mainly hydrolyze xylo-oligosaccharides by β-xylosidase activity. Moreover, the kinetic parameters of β-xylosidase and α-L-arabinofuranosidase of both two proteins indicated their affinity with all the detected natural substrate (CCX) and chromogenic substrates were nearly similar. In addition, despite having no signal peptides, both of them might export outside the cell by the nonconventional pathways. However, Ppxy143B exhibited wider temperature and pH ranges, higher pH and thermostability, and was less influenced by metal ions than Ppxyl43A. Given its enzymatic characteristics and predicted structure, it is likely that the C-terminus domain (GH43_C2) of Ppxyl43B enhances the stability of the two enzymes and also restricts the substrates’ or metal ions’ access to the active sites.ConclusionsPpxyl43A and Ppxyl43B were β-xylosidase/α-L-arabinofuranosidase bifunctional enzymes with different structures from Paenibacillus physcomitrellae XB and exhibited similar xylo-oligosaccharides hydrolyse ability, which would be useful in the further lignocellulosic biomass conversion.
Two Bifunctional β-Xylosidase /α-L-Arabinofuranosidases From GH43 With Different Structures in the xylan Degradation Strain of Paenibacillus Physcomitrellae XB Displayed the Similar xylo-oligosaccharides Degradation Ability