Cloning, expression, and characterization of novel GH5 endoglucanases from Thermobifida alba AHK119.

Thermobifida alba AHK119 exhibits sufficient filter paper-degradation activity in its culture supernatant. AHK119-bMs (1365 bp) and AHK119-E5 (1425 bp), which encode novel GH5 family endoglucanases, were cloned from the genomic DNA of T. alba AHK119. AHK119-bMs and AHK119-E5 consisted of 454 and 474 amino acid residues, respectively, in which the catalytic domain (CD) and carbohydrate-binding module (CBM) were connected by an accessary module (linker region). The amino acid sequences of CD and CBM of AHK119-bMs were most identical to those of endo-β-mannanases (Man5As) from Thermobifidafusca TM51, T. halotolerans YIM90462, and T.cellulosilytica TB100. In contrast, the amino acid sequences of CD and CBM of AHK119-E5 were most identical to those of endo-1,4-β-glucanases (cellulases; Cel5As) from T. fusca and T. halotolerans YIM90462. However, the linker region of both the genes shared low identities with those of Man5As and Cel5As. AHK119-bMs showed broader specificities toward cellulosic substrates than Man5As, whereas AHK119-E5 showed higher activity toward insoluble cellulosic substrates than toward soluble ones, which was conflicting when compared with other Cel5As. In addition, AHK119-bMs and AHK119-E5 showed different requirements for metal ions from those of Man5As and Cel5As, respectively. Therefore, both the enzymes were identified as novel GH5 endoglucanases, and the accessary modules seemed to play important roles in their enzymatic properties.