Structural Rationale for Differential Carbohydrate Recognition by Barley and Fibrobacter succinogenes 1,3-1,4-ß-D-Glucanases

Glycosyl hydrolase family 16 (GHF16) truncated Fibrobacter succinogenes (TFs) and GHF17 barley 1,3-1,4-beta-D-glucanases (beta-glucanases) catalyze the specific hydrolysis of beta-1,4 glycosidic bonds adjacent to beta-1,3 linkages in mixed beta-1,3 and beta-1,4 beta-D-glucans or lichenan. GHF17 banana beta-1,3-glucanase displays a conserved structural fold similar to that of barley 1,3-1,4-beta-D-glucanase, however, the enzymes cleave different beta-1,3 and beta-1,4 linked polysaccharides. In order to understand the structural rationale for the recognition of different polysaccharides by GHF 16 and 17 enzymes, we applied comparative modeling and structural analysis to study the protein-carbohydrate interaction and cleavage mechanism of these enzymes. Differences in the active site region residues of TFsbeta-glucanase and barley beta-glucanase create binding site topographies that require different substrate conformations. In contrast to barley beta-glucanase, TFsbeta-glucanase possesses a unique and compact active cleft site.