Novel fermentation/respiration switch protein regulated by enzyme IIA Glc in Escherichia coli

Abstract

The bacterial phosphoenolpyruvate:sugar phosphotransferase system regulates a variety of physiological processes as well as effecting sugar transport. The crr gene product (enzyme IIAGlc (IIAGlc)) mediates some of these regulatory phenomena. In this report, we characterize a novel IIA Glc-binding protein from Escherichia coli extracts, discovered using ligand-fishing with surface plasmon resonance spectroscopy. This protein, which we named FrsA (fermentation/respiration switch protein), is the 47-kDa product of the yafA gene, previously denoted as "function unknown." FrsA forms a 1:1 complex specifically with the unphosphorylated form of IIAGlc, with the highest affinity of any protein thus far shown to interact with IIAGlc. Orthologs of FrsA have been found to exist only in facultative anaerobes belonging to the γ-proteobacterial group. Disruption of frsA increased cellular respiration on several sugars including glucose, while increased FrsA expression resulted in an increased fermentation rate on these sugars with the concomitant accumulation of mixed-acid fermentation products. These results suggest that IIAGlc regulates the flux between respiration and fermentation pathways by sensing the available sugar species via a phosphorylation state-dependent interaction with FrsA.