Alpha-glucuronidase involved in the hydrolysis of xylan, a major structural heterogeneous polysaccharide found in plant biomass representing the second most abundant polysaccharide in the biosphere, after cellulose. Releases 4-O-methylglucuronic acid from xylan (By similarity). an alpha-D-glucuronoside + H2O = an alcohol + D-glucuronate Expressed in the presence of D-xylose and L-arabinose and at very low level in the presence of D-glucuronic acid. Expression is under the control of the xylanolytic transcriptional activator xlnR and the carbon catabolite repressor creA. Belongs to the glycosyl hydrolase 67 family.