Polyethylene glycols enhance the thermostability of β-cyclodextrin glycosyltransferase from Bacillus circulans

We investigated the ability of six polyethylene glycols (PEGs), with molecular weights ranging from 400 to 20,000 Da, to enhance the thermostability of β-cyclodextrin glycosyltransferase (β-CGTase) from Bacillus circulans. We found that PEGs with different molecular weights could activate and stabilize this β-CGTase, but to different degrees. The most significant increase (about 20%) in β-cyclodextrin-forming activity was achieved by adding 10-15% PEG 400. PEGs with low molecular weights also significantly enhanced the thermostability of β-CGTase; 15% PEG 1000 prolonged its half-life at 60°C by 6.5-fold, compared to a control. Fluorescence spectroscopy and circular dichroism analysis indicated that PEGs helped protect the tertiary and secondary structure of β-CGTase, respectively. This study provides an effective approach for improving the thermostability of CGTases and related enzymes.