Enhanced performance of cyclodextrin glycosyltransferase by immobilization on amine-induced macroporous metal organic framework

This study examined the effectiveness of a hierarchical copper-based metal–organic framework (H–Cu-BTC) in comparison with its microporous counterpart (Cu-BTC) for the immobilization of cyclodextrin glycosyltransferase (CGTase) for use in cyclodextrin production. The adsorption capacity, conformational changes, and operational stability of the immobilized enzymes were examined. The presence of both macropores and micropores in the proposed H–Cu-BTC resulted in an enhanced maximum adsorption capacity of 49.5 mg/g for CGTase as compared to 30.6 mg/g for Cu-BTC, which contains only micropores. The presence of macropores in H–Cu-BTC was also shown to more favorably affect the secondary structure of the immobilized enzyme. Using H–Cu-BTC, the proportion of β-sheets, which form the major structure in the protein and are responsible for the enzyme's stability, was shown to increase from 56% in free CGTase to 76.1% after immobilization. However, when using the microporous Cu-BTC, the proportion of β-sheets decreased to 44.1%. The favorable surface attachment of CGTase to H–Cu-BTC reflected its better reusability, wherein the activity was preserved up to 87% of the original CGTase activity after ten repeated cycles of reuse, compared to only 70% using Cu-BTC. The successful immobilization of CGTase on H–Cu-BTC demonstrated that it could be used as a robust biocatalyst for the conversion of starchy waste into cyclodextrins.