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Analysis of keystone enzyme in Agar hydrolysis provides insight into the degradation (of a polysaccharide from) red seaweeds.

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-?-(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.

SUBMITTER: Hehemann JH

PROVIDER: S-EPMC3340130 | biostudies-literature | 2012 Apr

REPOSITORIES: biostudies-literature

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Analysis of keystone enzyme in Agar hydrolysis provides insight into the degradation (of a polysaccharide from) red seaweeds.

Hehemann Jan-Hendrik JH Smyth Leo L Yadav Anuj A Vocadlo David J DJ Boraston Alisdair B AB

The Journal of biological chemistry 20120305 17

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 sho ...[more]

PMID: 22393053

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Project description:Models of benthic community dynamics for the extensively studied, shallow rocky ecosystems in eastern Canada emphasize kelp-urchin interactions. These models may bias the perception of factors and processes that structure communities, for they largely overlook the possible contribution of other seaweeds to ecosystem resilience. We examined the persistence of the annual, acidic (H2SO4), brown seaweed Desmarestia viridis in urchin barrens at two sites in Newfoundland (Canada) throughout an entire growth season (February to October). We also compared changes in epifaunal assemblages in D. viridis and other conspicuous canopy-forming seaweeds, the non-acidic conspecific Desmarestia aculeata and kelp Agarum clathratum. We show that D. viridis can form large canopies within the 2-to-8 m depth range that represent a transient community state termed "Desmarestia bed". The annual resurgence of Desmarestia beds and continuous occurrence of D. aculeata and A. clathratum, create biological structure for major recruitment pulses in invertebrate and fish assemblages (e.g. from quasi-absent gastropods to >150,000 recruits kg(-1) D. viridis). Many of these pulses phase with temperature-driven mass release of acid to the environment and die-off in D. viridis. We demonstrate experimentally that the chemical makeup of D. viridis and A. clathratum helps retard urchin grazing compared to D. aculeata and the highly consumed kelp Alaria esculenta. In light of our findings and related studies, we propose fundamental changes to the study of community shifts in shallow, rocky ecosystems in eastern Canada. In particular, we advocate the need to regard certain canopy-forming seaweeds as structuring forces interfering with top-down processes, rather than simple prey for keystone grazers. We also propose a novel, empirical model of ecological interactions for D. viridis. Overall, our study underscores the importance of studying organisms together with cross-scale environmental variability to better understand the factors and processes that shape marine communities.

Dataset Information

Analysis of keystone enzyme in Agar hydrolysis provides insight into the degradation (of a polysaccharide from) red seaweeds.

Publications

Analysis of keystone enzyme in Agar hydrolysis provides insight into the degradation (of a polysaccharide from) red seaweeds.

Similar Datasets

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