The Quaternary Structure of a Glycoside Hydrolase Dictates Specificity toward ?-Glucans.

ABSTRACT: In the Carbohydrate-Active Enzyme (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-?(1,4)-glucanase or ?(1,3;1,4)-glucanase activities. In this study, we focused on the GH5_26 enzyme fromSaccharophagus degradans(SdGluc5_26A), a marine bacterium known for its capacity to degrade a wide diversity of complex polysaccharides.SdGluc5_26A displays lichenase activity toward ?(1,3;1,4)-glucans with a side cellobiohydrolase activity toward ?(1,4)-glucans. The three-dimensional structure ofSdGluc5_26A adopts a stable trimeric quaternary structure also observable in solution. The N-terminal region ofSdGluc5_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 ofSdGluc5_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 ofSdGluc5_26A. Its deletion opens the enzyme cleft at the -3 subsite and turns the enzyme into an endo-?(1,4)-glucanase. This study demonstrates that experimental approaches can reveal structure-function relationships out of reach of current bioinformatic predictions.

SUBMITTER: Lafond M 

PROVIDER: S-EPMC4807298 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature