Fig. 7: Schematic model of virulence regulation by GrpP/GrpQ.

We proposed that once inside the urinary tracts, UPEC senses the presence of D-serine in urine through histidine kinase GrpP, which, in turn, transphosphorylates the response regulator GrpQ. Phosphorylated GrpQ directly binds to the fimS and activates the expression of type 1 fimbria, enabling UPEC to invade BECs and cause UTI.