Function and Expression of an N -Acetylneuraminic Acid-Inducible Outer Membrane Channel in Escherichia coli

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Abstract
The Escherichia coli yjhA (renamed nanC) gene encodes a protein of the KdgM family of outer membrane-specific channels. It is transcribed divergently from fimB , a gene involved in the site-specific inversion of the region controlling transcription of the fimbrial structural genes but is separated from it by one of the largest intergenic regions in E. coli . We show that nanC expression is induced by N -acetylneuraminic acid and modulated by N -acetylglucosamine. This regulation occurs via the NanR and NagC regulators, which also control fimB expression. nanC expression is also activated by the regulators cyclic AMP-catabolite activator protein, OmpR, and CpxR. When the NanC protein was reconstituted into liposomes, it formed channels with a conductance of 450 pS at positive potential and 300 to 400 pS at negative potential in 800 mM KCl. The channels had a weak anionic selectivity. In an ompR background, where the general porins OmpF and OmpC are absent, NanC is required for growth of E. coli on N -acetylneuraminic acid as the sole carbon source. All these results suggest that NanC is an N -acetylneuraminic acid outer membrane channel protein.