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

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Abstract
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.