Xenogeneic modulation of the ClpCP protease of Bacillus subtilis by a phage-encoded adaptor-like protein.

Like eukaryotic and archaeal viruses, which coopt the host's cellular pathways for their replication, bacteriophages have evolved strategies to alter the metabolism of their bacterial host. SPO1 bacteriophage infection of Bacillus subtilis results in comprehensive remodeling of cellular processes, leading to conversion of the bacterial cell into a factory for phage progeny production. A cluster of 26 genes in the SPO1 genome, called the host takeover module, encodes for potentially cytotoxic proteins that specifically shut down various processes in the bacterial host, including transcription, DNA synthesis, and cell division. However, the properties and bacterial targets of many genes of the SPO1 host takeover module remain elusive. Through a systematic analysis of gene products encoded by the SPO1 host takeover module, here we identified eight gene products that attenuated B. subtilis growth. Of the eight phage gene products that attenuated bacterial growth, a 25-kDa protein called Gp53 was shown to interact with the AAA+ chaperone protein ClpC of the ClpCP protease of B. subtilis Our results further reveal that Gp53 is a phage-encoded adaptor-like protein that modulates the activity of the ClpCP protease to enable efficient SPO1 phage progeny development. In summary, our findings indicate that the bacterial ClpCP protease is the target of xenogeneic (dys)regulation by a SPO1 phage-derived factor and add Gp53 to the list of antibacterial products that target bacterial protein degradation and therefore may have utility for the development of novel antibacterial agents.

A horse's eye view: size and shape discrimination compared with other mammals.

Mammals have adapted to a variety of natural environments from underwater to aerial and these different adaptations have affected their specific perceptive and cognitive abilities. This study used a computer-controlled touchscreen system to examine the visual discrimination abilities of horses, particularly regarding size and shape, and compared the results with those from chimpanzee, human and dolphin studies. Horses were able to discriminate a difference of 14% in circle size but showed worse discrimination thresholds than chimpanzees and humans; these differences cannot be explained by visual acuity. Furthermore, the present findings indicate that all species use length cues rather than area cues to discriminate size. In terms of shape discrimination, horses exhibited perceptual similarities among shapes with curvatures, vertical/horizontal lines and diagonal lines, and the relative contributions of each feature to perceptual similarity in horses differed from those for chimpanzees, humans and dolphins. Horses pay more attention to local components than to global shapes.

The Rsb Phosphoregulatory Network Controls Availability of the Primary Sigma Factor in Chlamydia trachomatis and Influences the Kinetics of Growth and Development.

Chlamydia trachomatis is an obligate intracellular human pathogen that exhibits stage-specific gene transcription throughout a biphasic developmental cycle. The mechanisms that control modulation in transcription and associated phenotypic changes are poorly understood. This study provides evidence that a switch-protein kinase regulatory network controls availability of σ66, the main sigma subunit for transcription in Chlamydia. In vitro analysis revealed that a putative switch-protein kinase regulator, RsbW, is capable of interacting directly with σ66, as well as phosphorylating its own antagonist, RsbV1, rendering it inactive. Conversely, the putative PP2C-like phosphatase domain of chlamydial RsbU was capable of reverting RsbV1 into its active state. Recent advances in genetic manipulation of Chlamydia were employed to inactivate rsbV1, as well as to increase the expression levels of rsbW or rsbV1, in vivo. Representative σ66-dependent gene transcription was repressed in the absence of rsbV1 or upon increased expression of RsbW, and increased upon elevated expression of RsbV1. These effects on housekeeping transcription were also correlated to several measures of growth and development. A model is proposed where the relative levels of active antagonist (RsbV1) and switch-protein anti-sigma factor (RsbW) control the availability of σ66 and subsequently act as a molecular 'throttle' for Chlamydia growth and development.

Systematic mutational analysis of the LytTR DNA binding domain of Staphylococcus aureus virulence gene transcription factor AgrA.

Most DNA-binding bacterial transcription factors contact DNA through a recognition α-helix in their DNA-binding domains. An emerging class of DNA-binding transcription factors, predominantly found in pathogenic bacteria interact with the DNA via a relatively novel type of DNA-binding domain, called the LytTR domain, which mainly comprises ß strands. Even though the crystal structure of the LytTR domain of the virulence gene transcription factor AgrA from Staphylococcus aureus bound to its cognate DNA sequence is available, the contribution of specific amino acid residues in the LytTR domain of AgrA to transcription activation remains elusive. Here, for the first time, we have systematically investigated the role of amino acid residues in transcription activation in a LytTR domain-containing transcription factor. Our analysis, which involves in vivo and in vitro analyses and molecular dynamics simulations of S. aureus AgrA identifies a highly conserved tyrosine residue, Y229, as a major amino acid determinant for maximal activation of transcription by AgrA and provides novel insights into structure-function relationships in S. aureus AgrA.

Cleavage of a putative metal permease in Chlamydia trachomatis yields an iron-dependent transcriptional repressor.

The regulation of iron homeostasis is essential for most organisms, because iron is required for a variety of conserved biochemical processes, yet can be toxic at high concentrations. Upon experiencing iron starvation in vitro, the obligate intracellular human pathogen Chlamydia trachomatis exhibits elevated expression of a putative iron-transport system encoded by the ytg operon. The third component of the ytg operon, CT069 (YtgCR), encodes a protein with two distinct domains: a membrane-anchored metal ion permease and a diphtheria toxin repressor (DtxR)-like transcriptional repressor. In this report, we demonstrate that the C-terminal domain of CT069 (YtgR) serves as an iron-dependent autorepressor of the ytg operon. Moreover, the nascent full-length metal permease-transcriptional repressor protein was processed during the course of infection, and heterologously when expressed in Escherichia coli. The products produced by heterologous cleavage in E. coli were functional in the repression of a reporter gene downstream of a putative YtgR operator. We report a bona fide mechanism of iron-dependent regulation of transcription in Chlamydia. Moreover, the unusual membrane permease-DNA-binding polypeptide fusion configuration was found in several bacteria. Therefore, the DNA-binding capability and liberation of the YtgR domain from a membrane-anchored permease in C. trachomatis could represent a previously uncharacterized mechanism for prokaryotic regulation of iron-homeostasis.