Energy-dependent conformational change in the To1A protein of Escherichia coli involves its N-terminal domain, To1Q, and To1R

TolQ, TolR, and TolA inner membrane proteins of Escherichia coli are involv ed in maintaining the stability of the outer membrane. They share homology with the ExbB, ExbD, and TonB proteins, respectively. The last is involved in energy transduction between the inner and the outer membrane, and its co nformation has been shown to depend on the presence of the proton motive fo rce (PMF), ExbB, and ExbD. Using limited proteolysis experiments, we invest igated whether the conformation of TolA was also affected by the PMF. We fo und that dissipation of the PMF by uncouplers led to the formation of a pro teinase K digestion fragment of TolA not seen when uncouplers are omitted. This fragment was also detected in Delta tolQ, Delta tolR, and tolA(H22P) m utants but, in contrast to the parental strain, was also seen in the absenc e of uncouplers. We repeated those experiments in outer membrane mutants su ch as lpp, pal, and Delta rfa, mutants: the behavior of TolA in lpp mutants was similar to that observed with the parental strain. However, the protei nase K-resistant fragment was never detected in the Delta rfa mutant. Altog ether, these results suggest that TolA is able to undergo a PMF-dependent c hange of conformation. This change requires TolQ, TolR, and a functional To lA N-terminal domain. The potential role of this energy-dependent process i n the stability of the outer membrane is discussed.