Biochemical and molecular characterization of secreted α-xylosidase from Aspergillus niger.
α-Linked xylose is a major component of xyloglucans in the cell walls of higher plants. An α-xylosidase (AxlA) was purified from a commercial enzyme preparation from Aspergillus niger, and the encoding gene was identified. The protein is a member of glycosyl hydrolase family 31. It was active on p-nitrophenyl-α-d-xyloside, isoprimeverose, xyloglucan heptasaccharide (XXXG), and tamarind xyloglucan. When expressed in Pichia pastoris, AxlA had activity comparable to the native enzyme on pNPαX and IP despite apparent hyperglycosylation. The pH optimum of AxlA was between 3.0 and 4.0. AxlA together with β-glucosidase depolymerized xyloglucan heptasaccharide. A combination of AxlA, β-glucosidase, xyloglucanase, and β-galactosidase in the optimal proportions of 51:5:19:25 or 59:5:11:25 could completely depolymerize tamarind XG to free Glc or Xyl, respectively. To the best of our knowledge, this is the first characterization of a secreted microbial α-xylosidase. Secreted α-xylosidases appear to be rare in nature, being absent from other tested commercial enzyme mixtures and from the genomes of most filamentous fungi.
Department of Energy Great Lakes Bioenergy Research Center and Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824, USA.
John S
JS
Scott-Craig
Melissa S
MS
Borrusch
Goutami
G
Banerjee
Christopher M
CM
Harvey
Jonathan D
JD
Walton
D001234:Aspergillus niger / Q000201:enzymology*; D044602:Cellulases / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D005696:Galactosidases / Q000378:metabolism; D005936:Glucans / Q000378:metabolism*; D005959:Glucosidases / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000378:metabolism; D010843:Pichia / Q000235:genetics / Q000378:metabolism; D029861:Tamarindus / Q000737:chemistry; D014990:Xylans / Q000378:metabolism*; D014995:Xylosidases / Q000235:genetics / Q000378:metabolism*
D005656:Fungal Proteins; D005936:Glucans; D014990:Xylans; C029353:xyloglucan; D044602:Cellulases; D005696:Galactosidases; D005959:Glucosidases; D006026:Glycoside Hydrolases; D014995:Xylosidases; C072818:xyloglucan endo(1-4)-beta-D-glucanase