CGTases

CGTases, or cyclodextrin glycosyltransferases, are enzymes that catalyze the conversion of starch into cyclodextrins. They perform transglycosylation reactions that cleave α-1,4 glycosidic bonds within glucan chains and re-link the fragments to form cyclic oligosaccharides. The major natural products are alpha-cyclodextrin (six glucose units), beta-cyclodextrin (seven units), and gamma-cyclodextrin (eight units). CGTases operate via a retaining mechanism that involves a covalent glycosyl-enzyme intermediate and belong to glycoside hydrolase family 13.

Source organisms and industrial relevance: CGTases are predominantly produced by certain Bacillus species, most notably Bacillus circulans, along with other Bacillus strains and thermophilic bacteria. Many CGTases are secreted enzymes used in large-scale manufacturing of cyclodextrins from starch.

Biochemical properties and reaction conditions: CGTases require starch as the glycosyl donor and can also process related glucans. They function over a range of pH values and temperatures, with thermostable variants adapted for high-temperature processes. Calcium ions are commonly reported to improve enzyme stability in some preparations. Product distribution among alpha-, beta-, and gamma-cyclodextrins is influenced by the enzyme source and reaction conditions, and by process design.

Applications and significance: Cyclodextrins produced by CGTases are valued for their ability to form inclusion complexes with a variety of hydrophobic compounds, enhancing solubility, stability, aroma, and delivery of active ingredients. They find uses in pharmaceuticals, food, cosmetics, and agriculture. Enzyme engineering and immobilization strategies are employed to tailor product selectivity and enable continuous production.