The structure and characterization of a modular endo-beta-1,4-mannanase from Cellulomonas fimi

The endo-β-1,4-mannanase from the soil bacterium Cellulomonas fimi is a modular plant cell wall degrading enzyme involved in the hydrolysis of the backbone of mannan, one of the most abundant polysaccharides of the hemicellulosic network in the plant cell wall. The crystal structure of a recombinant truncated endo-β-1,4-mannanase from C. fimi (CfMan26A-50K) was determined by X-ray crystallography to 2.25 A resolution using the molecular replacement technique. The overall structure of the enzyme consists of a core (β/α)8-barrel catalytic module characteristic of clan GH-A, connected via a linker to an immunoglobulin-like module of unknown function. A complex with the oligosaccharide mannotriose to 2.9 A resolution has also been obtained. Both the native structure and the complex show a cacodylate ion bound at the −1 subsite, while subsites −2, −3, and −4 are occupied by mannotriose in the complex. Enzyme kinetic analysis and the analysis of hydrolysis products from manno-oligosaccharides and mannopentitol ...