Comparative characterization of a bifunctional endo-1,4- β-mannanase/1,3-1,4- β-glucanase and its individual domains.

A fusion gene isolated from a microbial metagenome encodes a N-terminal endo-1,4- β-mannanase and a C-terminal 1,3-1,4- β -glucanase,. The full-length gene and the individual N- and C-domains were separately cloned and expressed in E coli. The purified whole enzyme hydrolyzed glucomannan, galactomannan, and β-glucan with Km and kcat values 2.2, 2.6, 3.6 mg/ml, and 302, 130, 337 min -1 , respectively. The hydrolysis of β-glucan by the C domain enzyme decreased significantly with added glucomannan to the reaction, suggesting inhibition effect. Analogous result was not observed with the N domain enzyme when β-glucan was added to the reaction. The whole enzyme did not show improvement of efficiency compared to the individual or additive total hydrolysis of the two domain enzymes using single or mixed substrates.