Substrate recognition and hydrolysis by a fungal xyloglucan-specific family 12 hydrolase.
Biochemical studies to elucidate the structural basis for xyloglucan specificity among GH12 xyloglucanases are lacking. Accordingly, the substrate specificity of a GH12 xyloglucanase from Aspergillus niger (AnXEG12A) was investigated using pea xyloglucan and 12 xylogluco-oligosaccharides, and data were compared to a structural model of the enzyme. The specific activity of AnXEG12A with pea xyloglucan was 113 micromol min(-1)mg(-1), and apparent k(cat) and K(m) values were 49 s(-1) and 0.54 mg mL(-1), respectively. These values are similar to previously published results using xyloglucan from tamarind seed, and suggest that substrate fucosylation does not affect the specific activity of this enzyme. AnXEG12A preferred xylogluco-oligosaccharides containing more than six glucose units, and with xylose substitution at the -3 and +1 subsites. The specific activities of AnXEG12A on 100 microM XXXGXXXG and 100 microM XLLGXLLG were 60+/-4 and 72+/-9 micromol min(-1)mg(-1), respectively. AnXEG12A did not hydrolyze XXXXXXXG, consistent with other data that demonstrate the requirement for an unbranched glucose residue for hydrolysis by this enzyme.
Powlowski
Justin
J
Department of Chemistry and Biochemistry, Concordia University, 7141 Sherbrooke St. West, Montreal, Quebec, Canada H4B 1R6.
Mahajan
Sonam
S
Schapira
Matthieu
M
Master
Emma R
ER
D001234:Aspergillus niger / Q000201:enzymology*; D002240:Carbohydrate Sequence; D005936:Glucans / Q000737:chemistry / Q000378:metabolism*; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000378:metabolism*; D006868:Hydrolysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018532:Pisum sativum / Q000737:chemistry; D011487:Protein Conformation; D013379:Substrate Specificity; D014990:Xylans / Q000737:chemistry / Q000378:metabolism*
D005936:Glucans; D014990:Xylans; C029353:xyloglucan; D006026:Glycoside Hydrolases; C072818:xyloglucan endo(1-4)-beta-D-glucanase