Importance of five amino acid residues at C-terminal region for the folding and stability of β-glucosidase of Cellvibrio gilvus

To determine the role of the C-terminal region of Cellvibrio gilvus β-glucosidase, a deletion mutant was constructed lacking five amino acid residues (RGRAR), three of which were arginine, from the C-terminal end. The mutant, designated ΔRGRAR, could be folded into an active form when expressed with the molecular chaperons $\text{GroEL}\text{ES}$. In comparison with the native enzyme, the optimum pH of the mutant ΔRGRAR shifted to the acidic region and the pH stability to the neutral region, while its heat stability decreased. No significant difference in the kinetic parameter K_m was observed. It was concluded that the RGRAR residues located at the C-terminal end are quite important for the stability of the enzyme and protein folding.