question: Which metabolite activates AtxA?
answer: Upon infection of a mammalian host, Bacillus anthracis responds to host cues, and particularly to elevated temperature (37°C) and bicarbonate/CO2 concentrations, with increased expression of virulence factors that include the anthrax toxins and extracellular capsular layer. Cultures grown with elevated CO(2) /bicarbonate exhibited increased AtxA dimer/monomer ratios and increased AtxA activity, relative to cultures grown without added CO(2) /bicarbonate, suggesting that this host-associated signal enhances AtxA function by shifting the dimer/monomer equilibrium towards the dimeric state. CO2-enhanced toxin gene transcription is not observed in atx4-null mutants. Overall data indicate a clear association of atxA with CO2-enhanced gene expression in B. anthracis and provide evidence that atxA regulates genes other than the structural genes for the anthrax toxin proteins.