The Membrane-Bound α-Glucuronidase from Pseudomonas cellulosa Hydrolyzes 4-O-Methyl-d-Glucuronoxylooligosaccharides but Not 4-O-Methyl-d-Glucuronoxylan

The microbial degradation of xylan is a key biological process. Hardwood 4-O-methyl-d-glucuronoxylans are extensively decorated with 4-O-methyl-d-glucuronic acid, which is cleaved from the polysaccharides by α-glucuronidases. In this report we describe the primary structures of the α-glucuronidase from Cellvibrio mixtus (C. mixtus GlcA67A) and the α-glucuronidase from Pseudomonas cellulosa (P. cellulosa GlcA67A) and characterize P. cellulosa GlcA67A. The primary structures of C. mixtus GlcA67A and P. cellulosa GlcA67A, which are 76% identical, exhibit similarities with α-glucuronidases in glycoside hydrolase family 67. The membrane-associated pseudomonad α-glucuronidase released 4-O-methyl-d-glucuronic acid from 4-O-methyl-d-glucuronoxylooligosaccharides but not from 4-O-methyl-d-glucuronoxylan. We propose that the role of the glucuronidase, in combination with cell-associated xylanases, is to hydrolyze decorated xylooligosaccharides, generated by extracellular hemicellulases, to xylose and 4-O-methyl-d-glucuronic acid, enabling the pseudomonad to preferentially utilize the sugars derived from these polymers.