Bacterial Sialate O-Acetyltransferases
- Pp. 209-235 (27)Martina Mühlenhoff and Anne K. Bergfeld
Several pathogenic bacteria decorate their cell surface with sialoglycoconjugates that in many cases mimic host structures and serve as important virulence factors. In addition to N-acetyl neuraminic acid, the prevalent sialic acid in the humans, O-acetylated sialic acids are observed in bacteria that carry acetyl groups at position C-7, C-8 and/or C-9. The ability to modify cell surface sialo-glycoconjugates by O-acetylation depends on the presence of sialate O-acetyltransferases, an enzyme class that catalyzes the transfer of acetyl groups from acetyl Coenzyme A to hydroxyl groups of either free or CMP-activated sialic acid or particularly sialylated carbohydrate structures. On the genetic level, distinct mechanisms were observed which lead to an ‘on/off’ switch of sialate O-acetyltransferase expression and/or modification of the enzymatic activity. The resulting changes in the degree of surface O-acetylation of these bacteria can lead to a huge structural variety that make them difficult targets for the immune system. Structural and biochemical analyzes demonstrated that bacterial sialate O-acetyltransferases evolved independently on two distinct structural frameworks, the left-handed β-helix fold and the α/β-hydrolase fold.