The siaA gene involved in capsule polysaccharide biosynthesis of Neisseria meningitidis B codes for N-acylglucosamine-6-phosphate 2-epimerase activity

FEMS Microbiol Lett. 2000 Mar 15;184(2):161-4. doi: 10.1111/j.1574-6968.2000.tb09008.x.


The capsule polysaccharide of Neisseria meningitidis serogroup B is composed of a homopolymer of alpha-2-->8 linked N-acetyl-neuraminic acid (sialic acid). The enzymes required for sialic acid biosynthesis and polymerization are encoded in region A of the capsule gene complex. We here describe the enzymatic activity of the siaA gene product as determined by biochemical analysis. siaA was overexpressed in Escherichia coli and the SiaA protein was purified to homogeneity. Enzymatic assays revealed that SiaA did not accept N-acetyl-glucosamine as substrate, but only N-acetyl-glucosamine-6-phosphate (EC SiaA catalyzes the isomerization of N-acetyl-glucosamine-6-phosphate to form N-acetyl-mannosamine-6-phosphate. This reaction represents the first step in capsule biosynthesis of N. meningitidis B.

MeSH terms

  • Acetylglucosamine / metabolism
  • Bacterial Capsules / biosynthesis*
  • Bacterial Capsules / chemistry
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Carbohydrate Epimerases / genetics*
  • Carbohydrate Epimerases / metabolism*
  • Genes, Bacterial
  • Isomerism
  • N-Acetylneuraminic Acid / metabolism
  • Neisseria meningitidis / genetics
  • Neisseria meningitidis / metabolism*
  • Racemases and Epimerases*
  • Recombinant Proteins / metabolism


  • Bacterial Proteins
  • Recombinant Proteins
  • Racemases and Epimerases
  • Carbohydrate Epimerases
  • NeuC protein, Neisseria meningitidis
  • N-acylglucosamine-6-phosphate 2-epimerase
  • N-Acetylneuraminic Acid
  • Acetylglucosamine