Sabatier Principle for Understanding Enzymatic Modification on Granular Starch

Interfacial enzyme reactions are a common occurrence in both natural biological processes and industrial applications, particularly in the enzymatic degradation during starch synthesis and utilization. There is significant interest in establishing a correlation between catalytic processes and the structural changes occurring on the surface of granular starches. To address this need, the Sabatier principle was employed to elucidate the relationship between enzymatic degradation and the granular structure of various maize starches. Initially, these maize starches underwent modifications by either branching enzyme (BE) or 4-α-glucanotransferase (4αGT), or they were sequentially modified by BE followed by 4αGT, resulting in the creation of modified starches (MSs) named MS-B, MS-T, and MS-BT, respectively. Structural analyses of the starches and molecular docking studies revealed that BE could catalyze transglycosylation on starch granules, whereas 4αGT could only catalyze disproportionation on MS-B, while exhibiting hydrolysis and/or cyclization activity on unmodified starches (NSs). The variations in the architecture of the active sites of these two enzymes most likely account for the observed differences. The active site of BE is open, allowing it to bind to chains on the surface of granular starch, whereas the partially closed active site of 4αGT restricts its transglycosylation activity on granular starches. Applying the Sabatier principle demonstrated that modifying starches using BE or 4αGT controls the binding affinity between the enzyme and starch, thereby influencing the catalytic rate. This research introduces a novel strategy for comprehending the enzymatic modification of starches by regulating binding affinity.