Evolutionary links between FliH/YscL-like proteins from bacterial type III secretion systems and second-stalk components of the FoF1 and vacuolar ATPases

Bacterial type III secretion drives flagellar biosynthesis and mediates bacterial-eukaryotic interactions. Type III secretion is driven by an ATPase that is homologous to the catalytic subunits of proton-translocating ATPases, such as the FoF1 ATPase. Here we use PSI-BLAST searches to show that some noncalatytic components are also conserved between type III secretion systems and proton-translocating ATPases. In particular, we show that the FliH/YscL-like proteins and the E subunits of vacuolar ATPases represent fusions of domains homologous to second-stalk components of the FoF1 ATPase (the b and delta subunits).