Joined: May 2002
Volume 49 Issue 2 Page 555 - July 2003
Identification of genes required for adventurous gliding motility in Myxococcus xanthus with the transposable element mariner
Philip Youderian 1 , Neal Burke 2 , David J. White 2 and Patricia L. Hartzell 2 *
Myxococcus xanthus glides over solid surfaces without the use of flagella, dependent upon two large sets of adventurous (A) and social (S) genes, using two different mechanisms of gliding motility. Myxococcus xanthus A S double mutants form non-motile colonies lacking migratory cells at their edges. We have isolated 115 independent mutants of M. xanthus with insertions of transposon magellan-4 in potential A genes by screening for insertions that reduce the motility of a mutant S parental strain. These insertions are found not only in the three loci known to be required for A motility, mglBA, cglB, and aglU, but also in 30 new genes. Six of these new genes encode different homologues of the TolR, TolB, and TolQ transport proteins, suggesting that adventurous motility is dependent on biopolymer transport. Other insertions which affect both A and S motility suggest that both systems share common energy and cell wall determinants. Because the spectrum of magellan-4 insertions in M. xanthus is extraordinarily broad, transposon mutagenesis with this eukaryotic genetic element permits the rapid genetic analysis of large sets of genes that contribute to a complex microbial behaviors such as A motility.
Among the genes identified in this study are those previously shown to be required for A-motility, cglB, aglU and mglA. Of the new genes identified, those whose products share similarity with TolQ, TolR, and TolB (aglS, aglT, aglU, aglV, aglW, aglX and aglY) comprise the largest group of genes whose products have related functions. The Tol proteins are known to function in transport and may encode structural components of the A-motility motor. The finding that homologues of Tol proteins are involved in A-motility is consistent with a model in which A motility is powered by the secretion of polyelectrolyte (Wolgemuth et al., 2002). In E. coli, TolA, TolQ and TolR interact to form a heteroligomeric membrane-associated macromolecular transport complex required for both biopolymer transport and outer membrane stability. The periplasmic TolB protein interacts with TolA and the outer membrane lipoprotein, Pal, to mediate contact between the inner and outer membranes (Walburger et al., 2002), which facilitates transport and maintains membrane integrity (Lazzaroni et al., 1999). In E. coli, mutations in tolB are pleiotropic, confer hypersensitivity to detergents, and result in the release of periplasmic proteins into the medium of growing cultures (Bouveret et al., 1995).
Combine that with...
Mol Microbiol. 2001 Nov;42(3):795-807. Related Articles, Links
The TolQ-TolR proteins energize TolA and share homologies with the flagellar motor proteins MotA-MotB.
Cascales E, Lloubes R, Sturgis JN.
Laboratoire d'Ingenierie de Systemes Macromoleculaires, Institut de Biologie Structurale et Microbiologie, CNRS, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
The Tol-Pal system of Escherichia coli is required for the maintenance of outer 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 system 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 interaction. A point mutation within the third transmembrane segment of TolQ was found to affect the TolA-Pal interaction strongly, whereas suppressor mutations within the TM segment of TolR restored this interaction. Modifying the Asp residue within the TM region of TolR indicated that an acidic residue was important for the pmf-dependent interaction of TolA with Pal and outer membrane stabilization. Analysis of sequence alignments of TolQ and TolR 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 ExbB and ExbD of the TonB system but also with MotA and MotB of the flagellar motor. The function of these three systems, as ion potential-driven molecular motors, is discussed
...and you've got the first genomic homology (of which I was aware) between bacterial flagella and gliding motility.
(although common descent of the systems still seems unlikely to me, at the least it would show that TolQR/ExbBD/MotAB-type proteins had been adapted as motility-related motors not just once but twice)