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

The capsule polysaccharide of Neisseria meningitidis serogroup B is compose d of a homopolymer of alpha-2 --> 8 linked N-acetyl-neuraminic acid (sialic acid). The enzymes required for sialic acid biosynthesis and polymerizatio n 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 a nalysis. siaA was overexpressed in Escherichia coli and the SiaA protein wa s purified to homogeneity. Enzymatic assays revealed that SiaA did not acce pt N-acetyl-glucosamine as substrate, but only N-acetyl-glucosamine-6-phosp hate (EC 5.1.3.9). SiaA catalyzes the isomerization of N-acetyl-glucosamine -6-phosphate to form N-acetyl-mannosamine-6-phosphate. This reaction repres ents the first step in capsule biosynthesis of N. meningitidis B. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Sci ence B.V. All rights reserved.