[Specific proteolysis of Clostridium thermocellum endoglucanase upon heterologous expression in Escherichia coli cells].

The cel(1) gene of Clostridium thermocellum encoding endoglucanase cloned earlier in Escherichia coli was deleted at specific sites and fused with the E. coli gene lacZ'. Analysis of heterologous expression of the produced variants was performed. It was established that the post-translational modification of the clostridial endoglucanase in E. coli involves a membrane-linked N-terminal cleavage of 6 kDa polypeptide during secretion through the cytoplasmic membrane and a C-terminal cleavage of 4 kDa protein not related to the secretion. A comparative study of the authors' and literature data supports the suggestions that: (i) the cel(1) cloned in this laboratory is a deleted variant of the cloned cel(1) gene of C. thermocellum described previously by other authors, and (ii) the C-terminal proteolysis of the endoglucanase precursor takes place in a linker region connecting the catalytic and cellulose binding domains. An account of similar kind of proteolysis responsible for multiple forms of cellulolytic enzymes is given.