Allosteric β-propeller signalling in TolB and its manipulation by translocating colicins

The Tol system is a five-protein assembly parasitized by colicins and bacteriophages that helps stabilize the Gram-negative outer membrane (OM). We show that allosteric signalling through the six-bladed beta-propeller protein TolB is central to Tol function in Escherichia coli and that this is subverted by colicins such as ColE9 to initiate their OM translocation. Protein-protein interactions with the TolB beta-propeller govern two conformational states that are adopted by the distal N-terminal 12 residues of TolB that bind TolA in the inner membrane. ColE9 promotes disorder of this 'TolA box' and recruitment of TolA. In contrast to ColE9, binding of the OM lipoprotein Pal to the same site induces conformational changes that sequester the TolA box to the TolB surface in which it exhibits little or no TolA binding. Our data suggest that Pal is an OFF switch for the Tol assembly, whereas colicins promote an ON state even though mimicking Pal. Comparison of the TolB mechanism to that of vertebrate guanine nucleotide exchange factor RCC1 suggests that allosteric signalling may be more prevalent in beta-propeller proteins than currently realized

The Tol/PAL and TonB systems : two envelope-spanning protein complexes involved in colicin import in E. coli.

International audienceMutants in tolA, B, Q, and R genes have been isolated on the basis of their tolerance to bacterial toxins (colicins) and their resistance to the infection of filamentous phages (Ml3, fd, and fl) (Davies and Reeves, 1975a, 1975b ; Nagel de Zwaig and Luria, 1967). These genes form a cluster at 16,8 min on the chromosomal map of E. coli. tol mutants are hypersensitive to detergents and to certain drugs, and they release periplasmic proteins into the growth medium (Nagel de Zwaig and Luria, 1967). Mutations in a contiguous gene, pal, which encodes the outer membrane Peptidoglycan Associated Lipoprotein (PAL), generate a similar phenotype (Fognini-Lefebvre et al., 1987). This suggests that the Tol/PAL proteins are involved in maintaining the integrity of the outer membrane of E. coli. However, the exact physiological role of the Tol/PAL system has not yet been elucidated

Genomes of ubiquitous marine and hypersaline Hydrogenovibrio, Thiomicrorhabdus, and Thiomicrospira spp. encode a diversity of mechanisms to sustain chemolithoautotrophy in heterogeneous environments.

Chemolithoautotrophic bacteria from the genera Hydrogenovibrio, Thiomicrorhabdus, and Thiomicrospira are common, sometimes dominant, isolates from sulfidic habitats including hydrothermal vents, soda and salt lakes, and marine sediments. Their genome sequences confirm their membership in a deeply branching clade of the Gammaproteobacteria. Several adaptations to heterogeneous habitats are apparent. Their genomes include large numbers of genes for sensing and responding to their environment (EAL- and GGDEF-domain proteins, and methyl-accepting chemotaxis proteins) despite their small sizes (2.1 - 3.1 Mbp). An array of sulfur-oxidizing complexes are encoded, likely to facilitate these organisms' use of multiple forms of reduced sulfur as electron donors. Hydrogenase genes are present in some taxa, including group 1d and 2b hydrogenases in Hydrogenovibrio marinus and H. thermophilus MA2-6, acquired via horizontal gene transfer. In addition to high-affinity cbb3cytochrome c oxidase, some also encode cytochrome bd-type quinol oxidase or ba3-type cytochrome c oxidase, which could facilitate growth under different oxygen tensions, or maintain redox balance. Carboxysome operons are present in most, with genes downstream encoding transporters from four evolutionarily distinct families, which may act with the carboxysomes to form CO2concentrating mechanisms. These adaptations to habitat variability likely contribute to the cosmopolitan distribution of these organisms. This article is protected by copyright. All rights reserved