Inulin fructotransferase (DFA-I-forming)

Inulin fructotransferase (DFA-I-forming) is an enzyme that catalyzes the transfer of fructosyl residues from inulin to other fructans, specifically resulting in the formation of di-fructosyl-anhydride (DFA-I). This enzyme plays a crucial role in the biosynthesis of fructans, a type of carbohydrate storage molecule found in various plants, including chicory, artichoke, and dahlia.

Function

The primary function of inulin fructotransferase (DFA-I-forming) is to synthesize DFA-I, a key building block in the larger inulin and fructan molecules. This enzyme acts by cleaving a terminal fructosyl residue from an inulin chain and transferring it to another inulin molecule, creating a new β(2→1) linkage which distinguishes DFA-I. The precise mechanism involves the formation of a covalent enzyme-fructosyl intermediate, followed by the transfer of the fructosyl group to the acceptor molecule. The specificity of the enzyme ensures that DFA-I, rather than other fructan structures, is primarily produced. This is vital for the control of the overall fructan chain length and branching patterns.

Biological Significance

The production of DFA-I by this enzyme is significant for several reasons:

• Fructan biosynthesis: DFA-I is a fundamental component in the construction of diverse fructan structures, contributing to their diverse functional roles in plants.
• Plant adaptation: Fructans function as energy reserves and play a role in stress tolerance (e.g., cold, drought). The efficient production of DFA-I by the enzyme is therefore linked to the overall fitness and survival of these plants.
• Prebiotic properties: Inulin and fructans, including DFA-I, are known for their prebiotic effects, promoting the growth of beneficial bacteria in the human gut. This enzyme's activity is thus relevant to food science and nutrition.

Specificity and Regulation

Inulin fructotransferases exhibit varying degrees of specificity for both donor and acceptor molecules. While the enzyme primarily creates DFA-I, it may also contribute to the formation of other fructan structures under certain conditions. Further research is needed to fully elucidate the factors that regulate the activity and specificity of this enzyme, including environmental cues and post-translational modifications.

Further Research

While much is known about the general role of inulin fructotransferase (DFA-I-forming) in fructan biosynthesis, further research is needed to fully understand the enzyme's precise mechanism, regulatory mechanisms, and its role in different plant species. Studies focusing on the enzyme's structure, catalytic kinetics, and genetic regulation will provide a more comprehensive picture of its function and importance.