LadS is a calcium-responsive kinase that induces acute-to-chronic virulence switch in Pseudomonas aeruginosa.

Virulence of pathogenic bacteria is a tightly controlled process to facilitate invasion and survival in host tissues. Although pathways controlling virulence have been defined in detail, signals modulating these processes are poorly understood. The opportunistic pathogen Pseudomonas aeruginosa causes acute and chronic infections in humans. Disease progression is typically associated with a loss of acute virulence and the emergence of biofilms and chronic behaviour. The acute-to-chronic switch is governed by the global Gac/Rsm pathway. Using a newly developed acute-chronic dual reporter system we show that calcium stimulates the Gac/Rsm pathway via the Gac-associated hybrid histidine kinase LadS. We show that calcium binds to the periplasmic DISMED2 sensor domain of LadS to activate its kinase activity. Activation of the Gac/Rsm pathway by calcium leads to a switch to the chronic program and confers drug tolerance by reducing P. aeruginosa growth rate. Clinical isolates from cystic fibrosis airways retain their calcium response during chronic infections. Our data imply that calcium sensing evolved as an adaptation to the opportunistic lifestyle of P. aeruginosa and that calcium serves as a host signal to balance acute-to-chronic behaviour during infections. Establishing calcium signalling in host-pathogen interaction adds to growing evidence indicating key roles for calcium in bacterial signalling.

Anomer-Specific Recognition and Dynamics in a Fucose-Binding Lectin.

Sugar binding by a cell surface ∼29 kDa lectin (RSL) from the bacterium Ralstonia solanacearum was characterized by NMR spectroscopy. The complexes formed with four monosaccharides and four fucosides were studied. Complete resonance assignments and backbone dynamics were determined for RSL in the sugar-free form and when bound to l-fucose or d-mannose. RSL was found to interact with both the α- and the ß-anomer of l-fucose and the "fucose like" sugars d-arabinose and l-galactose. Peak splitting was observed for some resonances of the binding site residues. The assignment of the split signals to the α- or ß-anomer was confirmed by comparison with the spectra of RSL bound to methyl-α-l-fucoside or methyl-ß-l-fucoside. The backbone dynamics of RSL were sensitive to the presence of ligand, with the protein adopting a more compact structure upon binding to l-fucose. Taking advantage of tryptophan residues in the binding sites, we show that the indole resonance is an excellent reporter on ligand binding. Each sugar resulted in a distinct signature of chemical shift perturbations, suggesting that tryptophan signals are a sufficient probe of sugar binding.

Insights into SCP/TAPS proteins of liver flukes based on large-scale bioinformatic analyses of sequence datasets.

BACKGROUND: SCP/TAPS proteins of parasitic helminths have been proposed to play key roles in fundamental biological processes linked to the invasion of and establishment in their mammalian host animals, such as the transition from free-living to parasitic stages and the modulation of host immune responses. Despite the evidence that SCP/TAPS proteins of parasitic nematodes are involved in host-parasite interactions, there is a paucity of information on this protein family for parasitic trematodes of socio-economic importance. METHODOLOGY/PRINCIPAL FINDINGS: We conducted the first large-scale study of SCP/TAPS proteins of a range of parasitic trematodes of both human and veterinary importance (including the liver flukes Clonorchis sinensis, Opisthorchis viverrini, Fasciola hepatica and F. gigantica as well as the blood flukes Schistosoma mansoni, S. japonicum and S. haematobium). We mined all current transcriptomic and/or genomic sequence datasets from public databases, predicted secondary structures of full-length protein sequences, undertook systematic phylogenetic analyses and investigated the differential transcription of SCP/TAPS genes in O. viverrini and F. hepatica, with an emphasis on those that are up-regulated in the developmental stages infecting the mammalian host. CONCLUSIONS: This work, which sheds new light on SCP/TAPS proteins, guides future structural and functional explorations of key SCP/TAPS molecules associated with diseases caused by flatworms. Future fundamental investigations of these molecules in parasites and the integration of structural and functional data could lead to new approaches for the control of parasitic diseases.

SBAL: a practical tool to generate and edit structure-based amino acid sequence alignments.

SUMMARY: Both alignment generation and visualization are important processes for producing biologically meaningful sequence alignments. Computational tools that combine reliable, automated and semi-automated approaches to produce secondary structure-based alignments with an appropriate visualization of the results are rare. We have developed SBAL, a tool to generate and edit secondary structure-based sequence alignments. It is easy to install and provides a user-friendly interface. Sequence alignments are displayed, with secondary structure assignments mapped to their corresponding regions in the sequence by using a simple colour scheme. The algorithm implemented for automated and semi-automated secondary structure-based alignment calculations shows a comparable performance to existing software. AVAILABILITY AND IMPLEMENTATION: SBAL has been implemented in Java to provide cross-platform compatibility. SBAL is freely available to academic users at http://www.structuralchemistry.org/pcsb/. Users will be asked for their name, institution and email address. A manual can also be downloaded from this site. The software, manual and test sets are also available as supplementary material. CONTACT: conan.wang@griffith.edu.au SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.