Identification and structural basis of an enzyme that degrades oligosaccharides in caramel

Cooking with fire produces foods containing carbohydrates that are not naturally occurring, such as α-d-fructofuranoside found in caramel. Each of the hundreds of compounds produced by caramelization reactions is considered to possess its own characteristics. Various studies from the viewpoints of biology and biochemistry have been conducted to elucidate some of the scientific characteristics. Here, we review the composition of caramelized sugars and then describe the enzymatic studies that have been conducted and the physiological functions of the caramelized sugar components that have been elucidated. In particular, we recently identified a glycoside hydrolase (GH), GH172 difructose dianhydride I synthase/hydrolase (αFFase1), from oral and intestinal bacteria, which is implicated in the degradation of oligosaccharides in caramel. The structural basis of αFFase1 and its ligands provided many insights. This discovery opened the door to several research fields, including the structural and phylogenetic relationship between the GH172 family enzymes and viral capsid proteins and the degradation of cell membrane glycans of acid-fast bacteria by some αFFase1 homologs. This review article is an extended version of the Japanese article, Identification and Structural Basis of an Enzyme Degrading Oligosaccharides in Caramel, published in SEIBUTSU BUTSURI Vol. 62, p. 184-186 (2022).