Catalyzes the depolymerization of methylglucuronoxylan (MeGAXn), a beta-1,4 xylan in which 10% to 20% of the xylose residues are substituted with alpha-1,2-4-O-methylglucuronate (MeGA) residues, which is predominant in hemicellulose fractions of hardwood and crop residues. Generates xylobiose (X2) and aldotetrauronate (MeGAX3) as the predominant products of MeGAXn hydrolysis; these products are then directly assimilated by the bacterium for subsequent metabolism. Thus, allows the bacterium to efficiently use polymeric MeGAXn as a growth substrate. Endohydrolysis of (1->4)-beta-D-xylosidic linkages in xylans. Optimum pH is 6.5 with sweet gum methylglucuronoxylan as substrate. Optimum temperature is 45 degrees Celsius with sweet gum methylglucuronoxylan as substrate. Glycan degradation; xylan degradation. Belongs to the glycosyl hydrolase 10 (cellulase F) family.