Structural highlights
FunctionPublication Abstract from PubMedIn the CAZy database, glycoside hydrolase family 5 (GH5) is a large family with more than 6,000 sequences. Among the 51 described GH5 subfamilies, subfamily GH5_26 contains members that display either endo- beta(1,4)-glucanase or beta(1,3;1,4)-glucanase activities. In this study, we focused on the GH5_26 enzyme from Saccharophagus degradans (SdGluc5_26A) a marine bacterium known for its capacity to degrade a wide diversity of complex polysaccharides. SdGluc5_26A displays lichenase activity towards beta(1,3;1,4)-glucans with a side cellobiohydrolase activity towards beta(1,4)-glucans. The 3D structure of SdGluc5_26A adopts a stable trimeric quaternary structure observable also in solution. The N-terminal region of SdGluc5_26A protrudes into the active site of an adjacent monomer. To understand whether this occupation of the active site could influence its activity, we conducted a comprehensive enzymatic characterization of SdGluc5_26A and of a mutant truncated at the N-terminus. Ligand complex structures and kinetic analyses reveal that the N-terminus governs the substrate specificity of SdGluc5_26A. Its deletion opens the enzyme cleft at the -3 subsite and turns the enzyme into an endo-beta(1,4)-glucanase. This study demonstrates that experimental approaches can reveal structure-function relationships out of reach of current bioinformatic predictions. the quaternary structure of a glycoside hydrolase dictates specificity towards beta-glucans.,Lafond M, Sulzenbacher G, Freyd T, Henrissat B, Berrin JG, Garron ML J Biol Chem. 2016 Jan 11. pii: jbc.M115.695999. PMID:26755730[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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