4ce7
Crystal structure of a novel unsaturated beta-glucuronyl hydrolase enzyme, belonging to family GH105, involved in ulvan degradation
Structural highlights
FunctionUH105_NONUL Glucuronyl hydrolase involved in ulvan degradation. Ulvan is the main polysaccharide component of the Ulvales (green seaweed) cell wall. It is composed of disaccharide building blocks comprising 3-sulfated rhamnose (Rha3S) linked to D-glucuronic acid (GlcA), L-iduronic acid (IduA), or D-xylose (Xyl). Unsaturated 3S-rhamnoglycuronyl hydrolase works together with ulvan lyases to fully degrade the ulvan polymer, catalyzing specifically the cleavage of the unsaturated 4-deoxy-L-threo-hex-4-enopyranosiduronic acid (deltaUA) of deltaUA-Rha3S disaccharides and deltaUA-Rha3S-Xyl-Rha3S tetrasaccharides, the end products of the ulvan lyase reaction. Also hydrolases deltaUA-Rha3S-IduA-Rha3S and deltaUA-Rha3S-GlcA-Rha3S tetrasaccharidestetrasaccharides. Prefers tetrasaccharides over disaccharides and prefers an uronic residue at subsite +2.[1] Publication Abstract from PubMedUlvans 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 beta-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 E. coli, and enzymology experiments demonstrated its unsaturated beta-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 3D 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 beta-glucuronyl hydrolase is part of a previously uncharacterized subgroup of GH105 members and exhibits only a very limited sequence similarity to known unsaturated alpha-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 alpha- or beta-configuration of the cleaved linkage. A novel unsaturated beta-glucuronyl hydrolase involved in ulvan degradation unveils the versatility of stereochemistry requirements in family GH105.,Nyvall-Collen P, Jeudy A, Sassi JF, Groisillier A, Czjzek M, Coutinho PM, Helbert W J Biol Chem. 2014 Jan 9. PMID:24407291[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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