The ToIQ-ToIR proteins energize ToIA and share homologies with the flagellar motor proteins MotA-MotB

Cascales, E Lioubes, R Sturgis, JN

E. Cascales et al., The ToIQ-ToIR proteins energize ToIA and share homologies with the flagellar motor proteins MotA-MotB, MOL MICROB, 42(3), 2001, pp. 795-807

66

INGLESE

Article

Microbiology

MOLECULAR MICROBIOLOGY

0950-382X → ACNP

42

3

2001

795 - 807

ISI

0950-382X(200111)42:3<795:TTPETA>2.0.ZU;2-3

The Tol-Pal system of Escherichia coli is required for the maintenance of o uter membrane stability. Recently, proton motive force (pmf) has been found to be necessary for the co-precipitation of the outer membrane lipoprotein Pal with the inner membrane TolA protein, indicating that the Tol-Pal syst em forms a transmembrane link in which TolA is energized. In this study, we show that both TolQ and TolR proteins are essential for the TolA-Pal inter action. A point mutation within the third transmembrane (TM) segment of Tol Q was found to affect the TolA-Pal interaction strongly, whereas suppressor mutations within the TM segment of TolR restored this interaction. Modifyi ng the Asp residue within the TM region of TolR indicated that an acidic re sidue was important for the pmf-dependent interaction of TolA with Pal and outer membrane stabilization. Analysis of sequence alignments of TolQ and T olR homologues from numerous Gram-negative bacterial genomes, together with analyses of the different tolQ-tolR mutants, revealed that the TM domains of TolQ and TolR present structural and functional homologies not only to E xbB and ExbD of the TonB system but also with MotA and MotB of the flagella r motor. The function of these three systems, as ion potential-driven molec ular motors, is discussed.