Purification and properties of two truncated endoglucanases produced in Escherichia coli harbouring Clostridium cellulolyticum endoglucanase gene celCCD

The endoglucanase gene, celCCD, of Clostridium cellulolyticum has been expressed in Escherichia coli. Multiple active polypeptides were detected in the E. coli cells. The relative molecular mass (M_r) of two major active polypeptides were 56 000 (D56) and 38 000 (D38), which were smaller than the deduced M_r of the mature protein (63 401). D56 and D38 were purified from the periplasmic fraction. The N-terminal sequences of the two purified polypeptides were identical to that of the mature endoglucanase (Ala-Ile-Asn-Ser-Gln-Asp-Met-Val---) deduced from the nucleotide sequence. These data indicated that these polypeptides were produced by processing the original mature protein in the C-terminal region. The enzymatic properties of these two polypeptides were very similar, except that the specific activity of D38 was 2–3.5-fold higher than that of D56, and D38 was more heat stable than D56.