FIG 8 .

Model of sensing of periplasmic aspartate by GlnH: Asp leads to activation of PknG and derepression of the TCA cycle. In the absence of extracellular amino acids, GarA inhibits catabolism of glutamate through the TCA cycle. In contrast, the presence of aspartate causes conformational change of the sensor GlnH, leading to conformational change of GlnX that activates PknG. PknG becomes autophosphorylated and phosphorylates GarA, thus relieving inhibition of the TCA cycle.