NeuA O-acetylesterase activity is specific for CMP-activated O-acetyl sialic acid in Streptococcus suis serotype 2.

Abstract Several bacteria causing meningitis, such as Escherichia coli K1, Streptococcus suis , Neisseria meningitidis , and group B Streptococci (GBS), produce sialic acid (Neu5Ac)-containing capsular polysaccharide (CPS). Biosynthesis of the Neu5Ac-containing CPS requires CMP-Neu5Ac as substrate, which is synthesized by CMP-Neu5Ac synthetase from CTP and Neu5Ac. In E. coli or GBS, the NeuA protein encoded by the neuA gene has been known encoding a bifunctional enzyme that possesses both CMP-Neu5Ac synthetase and O -acetylesterase activity. In this report, we found that the S. suis NeuA ( Ss NeuA) was also a bifunctional CMP-Neu5Ac synthetase/ O -acetylesterase. Biochemical analyses revealed that the Ss NeuA strictly de- O -acetylated CMP- O -acetyl-Neu5Ac, whereas the E. coli NeuA ( Ec NeuA) preferentially de-O-acetylated CMP- O -acetyl-Neu5Ac. E. coli devoid of NeuA O -acetylesterase activity was unable to produce capsule and only CMP-Neu5Ac synthetase activity of the Ec NeuA or Ss NeuA could not restore its ability to produce capsule . These results suggest that the O -acetylesterase is essential for the synthesis of capsular Neu5Ac in E. coli , probably in S. suis and GBS as well. Our findings are key to understanding the biosynthesis of capsular Neu5Ac in E. coli , S. suis and GBS.