Common Evolutionary Origin for the Rotor Domain of Rotary Atpases and Flagellar Protein Export Apparatus

The V(1)- and F(1)- rotary ATPases contain a rotor that rotates against a catalytic A(3)B(3) or α(3)β(3) stator. The rotor F(1)-γ or V(1)-DF is composed of both anti-parallel coiled coil and globular-loop parts. The bacterial flagellar type III export apparatus contains a V(1)/F(1)-like ATPase ring structure composed of FliI(6) homo-hexamer and FliJ which adopts an anti-parallel coiled coil structure without the globular-loop part. Here we report that FliJ of Salmonella enterica serovar Typhimurium shows a rotor like function in Thermus thermophilus A(3)B(3) based on both biochemical and structural analysis. Single molecular analysis indicates that an anti-parallel coiled-coil structure protein (FliJ structure protein) functions as a rotor in A(3)B(3). A rotary ATPase possessing an F(1)-γ-like protein generated by fusion of the D and F subunits of V(1) rotates, suggesting F(1)-γ could be the result of a fusion of the genes encoding two separate rotor subunits. Together with sequence comparison among the globular part proteins, the data strongly suggest that the rotor domains of the rotary ATPases and the flagellar export apparatus share a common evolutionary origin.