Characterization of a cellulose binding domain from Clostridium cellulovorans endoglucanase-xylanase D and its use as a fusion partner for soluble protein expression in Escherichia coli

Different chimeric proteins combining the non-catalytic C-terminal putative cellulose binding domain of Clostridium cellulovorans endoglucanase-xylanase D (EngD) with its proline-threonine rich region PT-linker, PTCBDEngD, cellulose binding domain of C. cellulovorans cellulose binding protein A, CBDCbpA, cohesin domains Cip7, Coh6 and CipC1 from different clostridial species and recombinant antibody binding protein LG were constructed, expressed, purified and analyzed. The solubilities of chimeric proteins containing highly soluble domains Cip7, CipC1 and LG were not affected by fusion with PTCBDEngD. Insoluble domain Coh6 was solubilized when fused with PTCBDEngD. In contrast, fusion with CBDCbpA resulted in only a slight increase in solubility of Coh6 and even decreased solubility of CipC1 greatly. PTCBDEngD and Cip7-PTCBDEngD were shown to bind regenerated commercial amorphous cellulose Cuprophan. The purity of Cip7-PTCBDEngD eluted from Cuprophan was comparable to that purified by conventional ion exchange chromatography. The results demonstrated that PTCBDEngD can serve as a bi-functional fusion tag for solubilization of fusion partners and as a domain for the immobilization, enrichment and purification of molecules or cells on regenerated amorphous cellulose.