Catalytic and thermodynamic properties of glycosylated Bacillus cereus cyclodextrin glycosyltransferase

• Evaluation of the stability of conjugates of CGTase with several oxidized polysaccharides.
• The conjugated enzyme showed enhanced thermal and pH stability.
• The conjugated enzyme showed lower inactivation rate constant with increased half life.
• The conjugated enzyme showed higher vales for the energy for irreversible thermal inactivation.
• The conjugated CGTase showed lower vales of ΔH*, ΔG*, ΔS*, ΔG*E−S, and ΔG*T−S.
• The conjugated CGTase showed significant impact on improvement of kcat, kcat/Km values.
• Both the native and conjugated CGTase produced cyclodextrin form starch of α-type.

Cyclodextrin glycosyltransferase (CGTase) was covalently coupled to five oxidized polysaccharides differing in structure and chemical nature. The conjugates were evaluated for the retained activity, kinetic and thermodynamic stability. The conjugated CGTase with oxidized dextran (MW 47000) had the highest retained specific activity (70.05%) and the highest half-life (T1/2) at 80 °C. Compared to the native enzyme, the conjugated preparation exhibited higher optimum temperature, lower activation energy (Ea), lower deactivation constant rate (kd), higher T1/2, and higher D values (decimal reduction time) within the temperature range of 60–80 °C. The values of thermodynamic parameters for irreversible inactivation of native and conjugated CGTase indicated that conjugation significantly decreased entropy (ΔS*) and enthalpy of deactivation (ΔH*). The results of thermodynamic analysis for cyclodextrin production from starch indicated that The enthalpy of activation (ΔH*) and free energy of activation (ΔG*), (free energy of transition state) ΔG*E–T and (free energy of substrate binding) ΔG*E–S values were lower for the conjugated CGTase. Similarly, there was significant impact on improvement of kcat, kcat/Km values. Both native and conjugated enzyme produce α-cyclodextrin from starch.