The structural basis for catalysis and specificity of the Pseudomonas cellulosa alpha-glucuronidase, GlcA67A.
Alpha-glucuronidases, components of an ensemble of enzymes central to the recycling of photosynthetic biomass, remove the alpha-1,2 linked 4-O-methyl glucuronic acid from xylans. The structure of the alpha-glucuronidase, GlcA67A, from Pseudomonas cellulosa reveals three domains, the central of which is a (beta/alpha)(8) barrel housing the catalytic apparatus. Complexes of the enzyme with the individual reaction products, either xylobiose or glucuronic acid, and the ternary complex of both glucuronic acid and xylotriose reveal a "blind" pocket which selects for short decorated xylooligosaccharides substituted with the uronic acid at their nonreducing end, consistent with kinetic data. The catalytic center reveals a constellation of carboxylates; Glu292 is poised to provide protonic assistance to leaving group departure with Glu393 and Asp365 both appropriately positioned to provide base-catalyzed assistance for inverting nucleophilic attack by water.
Nurizzo
Didier
D
Structural Biology Laboratory, Department of Chemistry, The University of York, Heslington, United Kingdom.
Nagy
Tibor
T
Gilbert
Harry J
HJ
Davies
Gideon J
GJ
D001665:Binding Sites; D018360:Crystallography, X-Ray; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000378:metabolism*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011549:Pseudomonas / Q000201:enzymology*; D013379:Substrate Specificity
D008024:Ligands; D006026:Glycoside Hydrolases; C096734:alpha-glucuronidase