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PDBsum entry 4ce7
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References listed in PDB file
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Key reference
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Title
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A novel unsaturated β-Glucuronyl hydrolase involved in ulvan degradation unveils the versatility of stereochemistry requirements in family gh105.
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Authors
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P.N.Collén,
A.Jeudy,
J.F.Sassi,
A.Groisillier,
M.Czjzek,
P.M.Coutinho,
W.Helbert.
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Ref.
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J Biol Chem, 2014,
289,
6199-6211.
[DOI no: ]
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PubMed id
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Abstract
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Ulvans are cell wall matrix polysaccharides in green algae belonging to the
genus Ulva. Enzymatic degradation of the polysaccharide by ulvan lyases leads to
the production of oligosaccharides with an unsaturated β-glucuronyl residue
located at the non-reducing end. Exploration of the genomic environment around
the Nonlabens ulvanivorans (previously Percicivirga ulvanivorans) ulvan lyase
revealed a gene highly similar to known unsaturated uronyl hydrolases classified
in the CAZy glycoside hydrolase family 105. The gene was cloned, the protein was
overexpressed in Escherichia coli, and enzymology experiments demonstrated its
unsaturated β-glucuronyl activity. Kinetic analysis of purified oligo-ulvans
incubated with the new enzyme showed that the full substrate specificity is
attained by three subsites that preferentially bind anionic residues (sulfated
rhamnose, glucuronic/iduronic acid). The three-dimensional crystal structure of
the native enzyme reveals that a trimeric organization is required for substrate
binding and recognition at the +2 binding subsite. This novel unsaturated
β-glucuronyl hydrolase is part of a previously uncharacterized subgroup of
GH105 members and exhibits only a very limited sequence similarity to known
unsaturated β-glucuronyl sequences previously found only in family GH88. Clan-O
formed by families GH88 and GH105 was singular in the fact that it covered
families acting on both axial and equatorial glycosidic linkages, respectively.
The overall comparison of active site structures between enzymes from these two
families highlights how that within family GH105, and unlike for classical
glycoside hydrolysis, the hydrolysis of vinyl ether groups from unsaturated
saccharides occurs independently of the α or β configuration of the cleaved
linkage.
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