New insight into characteristics, and substrate specificity of GH51 endogluanase and α-L-arabinofuranosidase from Alicyclobacillus sp. A4

The cellulose-degrading bacteria produce a battery of enzymes with different specificities, which act together in synergism. To effectively degrade the plant cell wall complex, another strategy is to induce the multifunctionalization of certain enzymes to hydrolyze different kinds of substrates. The thermoacidophilic Alicyclobacillus sp. A4 isolated from hot spring in china has been reported produce cellulose and hemicellulose enzymes. The extremely acidic endoglucanase, CelA4, belonging to glycoside hydrolase (GH) familie 51 was expressed and characterized. It displayed broad substrate specificities. CelA4 most active on barley â-glucan, moderate on CMC-Na and beechwood xylan. Surprisingly, CelA4 was also most active on xyloglucan, so this result showed GH 51 endoglucanases were new type of xyloglucanases. Further, the other novel GH 51 gene (abfA4) was expressed and characterized. AbfA4 also had widely enzyme activities for different types of substrates. For 10 min reaction, AbfA4 only showed high a-L-Arabinofuranosidase activity and no â-xylosidase activity. But for long time reaction (12 h), AbfA4 exhibited activity against sugar beet arabinan, debranched sugar beet arabinan, these results showed AbfA4 able to access the O-3 and O-2 linked arabinofuranose side chains and linear non-subsituted arabinan. Interestingly, the hydrolysis products of water-soluble wheat arabinoxylan produced by AbfA4 were arabinan, and xylooligosaccharides. These results showed AbfA4 had ability to remove the side chain decorations and cleave the main chain on xylans, so AbfA4 had xylanase activity. Our results increase the variety of GH51 enzymes and may assist in research on enzymatic hydrolysis of plant cell walls.