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Analysis of Keystone Enzyme in Agar Hydrolysis Provides Insight into the Degradation of a Polysaccharide from Red Seaweeds.
- Source :
-
Journal of Biological Chemistry . 4/20/2012, Vol. 287 Issue 17, p13985-13995. 11p. - Publication Year :
- 2012
-
Abstract
- Agars are abundant polysaccharides from marine red algae, and their chemical structure consists of alternating D-galactose and 3,6-anhydro-L-galactose residues, the latter of which are presumed to make the polymer recalcitrant to degradation by most terrestrial bacteria. Here we study a family 117 glycoside hydrolase (BpGH117) encoded within a recently discovered locus from the human gut bacterium Bacteroides plebeius. Consistent with this locus being involved in agarocolloid degradation, we show that BpGH117 is an exo-acting 3,6-anhydro-L- (1,3)-L-galactosidase that removes the 3,6-anhydrogalactose from the non-reducing end of neoagaro-oligosaccharides. A Michaelis complex of BpGH117 with neoagarobiose reveals the distortion of the constrained 3,6-anhydro-L-galactose into a conformation that favors catalysis. Furthermore, this complex, supported by analysis of site-directed mutants, provides evidence for an organization of the active site and positioning of the catalytic residues that are consistent with an inverting mechanism of catalysis and suggests that a histidine residue acts as the general acid. This latter feature differs from the vast majority of glycoside hydrolases, which use a carboxylic acid, highlighting the alternative strategies that enzymes may utilize in catalyzing the cleavage of glycosidic bonds. [ABSTRACT FROM AUTHOR]
- Subjects :
- *AGAR
*POLYSACCHARIDES
*RED algae
*GALACTOSE
*GLYCOSIDASES
*OLIGOSACCHARIDES
Subjects
Details
- Language :
- English
- ISSN :
- 00219258
- Volume :
- 287
- Issue :
- 17
- Database :
- Academic Search Index
- Journal :
- Journal of Biological Chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 74656979
- Full Text :
- https://doi.org/10.1074/jbc.M112.345645