Crystal Structure Analysis of the Polysialic Acid Specific O-Acetyltransferase NeuO
Figure 6
Proposed reaction mechanism for polySia O-acetylation catalyzed by NeuO.
Activation of the hydroxyl group at position C7 or C9 of the sialic acid moiety currently positioned in the active site of NeuO facilitates nucleophilic attack of the thioester carbonyl of acetyl-CoA. This leads to the formation of a sialyl-CoA intermediate with Arg137 stabilizing the oxyanion. Decomposition of the tetrahedral intermediate results in release of free CoA and O-acetylated polySia. During this step, His147 protonates the sulfur atom of CoA and a new cycle of acetylation can begin.