An Archaeal Cyclodextrin Glycosyltransferase from Haloferax sp.: Characterization and Application in Starch Degradation

Cyclodextrin glycosyltransferase (CGTase) is a highly valuable biocatalyst in industrial starch conversion, particularly for the synthesis of cyclic oligosaccharides. In this study, a CGTase, designated HfCGT, was cloned from Haloferax sp. and heterologously expressed in Escherichia coli. The recombinant enzyme was purified and biochemically characterized. HfCGT exhibited maximal catalytic activity at 70 °C and pH 8.0, tolerance to metal ions and EDTA, and enhanced activity in the presence of 1 M NaCl and Ca2+. High-performance liquid chromatography (HPLC) and high-resolution mass spectrometry (HRMS) analyses revealed that the starch products by HfCGT degradation were mainly large-ring cyclodextrins (LR-CDs) with polymerization degrees of 9 to 20. Altogether, the thermostability, haloalkaliphilic, and distinctive product profile make HfCGT a promising biocatalyst for pharmaceutical, food, and biotechnological applications.