▪ Abstract Most prokaryotic signal-transduction systems and a few eukaryotic pathways use phosphotransfer schemes involving two conserved components, a histidine protein kinase and a response regul...

Two-component signal transduction

The accessory genes of Staphylococcus aureus, including those involved in pathogenesis, are controlled by a complex regulatory network that includes at least four two-component systems, one of which, agr, is a quorum sensor, an alternative sigma factor and a large set of transcription factors, including at least two of the superantigen genes, tst and seb. These regulatory genes are hypothesized to act in a time- and population density-dependent manner to integrate signals received from the external environment with the internal metabolic machinery of the cell, in order to achieve the production of particular subsets of accessory/virulence factors at the time and in quantities that are appropriate to the needs of the organism at any given location. From the standpoint of pathogenesis, the regulatory agenda is presumably tuned to particular sites in the host organism. To address this hypothesis, it will be necessary to understand in considerable detail the regulatory interactions among the organism's numerous controlling systems. This review is an attempt to integrate a large body of data into the beginnings of a model that will hopefully help to guide research towards a full-scale test.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2958.2003.03526.x

Autoinduction and signal transduction in the regulation of staphylococcal virulence

Teichoic acids (TAs) are major wall and membrane components of most gram-positive bacteria. With few exceptions, they are polymers of glycerol-phosphate or ribitol-phosphate to which are attached glycosyl and d-alanyl ester residues. Wall TA is attached to peptidoglycan via a linkage unit, whereas lipoteichoic acid is attached to glycolipid intercalated in the membrane. Together with peptidoglycan, these polymers make up a polyanionic matrix that functions in (i) cation homeostasis; (ii) trafficking of ions, nutrients, proteins, and antibiotics; (iii) regulation of autolysins; and (iv) presentation of envelope proteins. The esterification of TAs with d-alanyl esters provides a means of modulating the net anionic charge, determining the cationic binding capacity, and displaying cations in the wall. This review addresses the structures and functions of d-alanyl-TAs, the d-alanylation system encoded by the dlt operon, and the roles of TAs in cell growth. The importance of dlt in the physiology of many organisms is illustrated by the variety of mutant phenotypes. In addition, advances in our understanding of d-alanyl ester function in virulence and host-mediated responses have been made possible through targeted mutagenesis of dlt. Studies of the mechanism of d-alanylation have identified two potential targets of antibacterial action and provided possible screening reactions for designing novel agents targeted to d-alanyl-TA synthesis.

A Continuum of Anionic Charge: Structures and Functions of d-Alanyl-Teichoic Acids in Gram-Positive Bacteria

Reaction mechanism of alkaline phosphatase based on crystal structures. Two-metal ion catalysis.

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5′-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.

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Cellular function and molecular structure of ecto-nucleotidases

Two Bacillus subtilis genes, designated resD and resE, encode proteins that are similar to those of two-component signal transduction systems and play a regulatory role in respiration. The overlapping resD-resE genes are transcribed during vegetative growth from a very weak promoter directly upstream of resD. They are also part of a larger operon that includes three upstream genes, resABC (formerly orfX14, -15, and -16), the expression of which is strongly induced postexponentially. ResD is required for the expression of the following genes: resA, ctaA (required for heme A synthesis), and the petCBD operon (encoding subunits of the cytochrome bf complex). The resABC genes are essential genes which encode products with similarity to cytochrome c biogenesis proteins. resD null mutations are more deleterious to the cell than those of resE. resD mutant phenotypes, directly related to respiratory function, include streptomycin resistance, lack of production of aa3 or caa3 terminal oxidases, acid accumulation when grown with glucose as a carbon source, and loss of ability to grow anaerobically on a medium containing nitrate. A resD mutation also affected sporulation, carbon source utilization, and Pho regulon regulation. The data presented here support an activation role for ResD, and to a lesser extent ResE, in global regulation of aerobic and anaerobic respiration i B.subtilis.

Regulators of aerobic and anaerobic respiration in Bacillus subtilis.

Depletion of nutrients, including phosphate, is a stress often encountered by a bacterial cell, and results in slowed growth, marking the cessation of exponential growth. Genes that are transcriptionally activated during phosphate starvation have been used to examine the signal-transduction mechanisms governing the Pho regulon in Bacillus subtilis. Alkaline phosphatase, the traditional reporter protein for Pho regulation in prokaryotes, is encoded by a multigene family in B. subtilis. Characterization of the alkaline phosphatase family was a breakthrough in the study of regulation of the Pho regulon, especially the discovery of promoter elements exclusively responsive to phosphate-starvation regulation. Current data suggest that at least three two-component signal-transduction systems interact, forming a regulatory network that controls the phosphate-deficiency response in B. subtilis. The interconnected pathways involve the PhoP-PhoR system, whose primary role is to mediate the phosphate-deficiency response; the SpoO phosphorelay required for the initiation of sporulation; and a newly discovered signal-transduction system, ResD-ResE, which also has a role in respiratory regulation during late growth. Parallel pathways positively regulate the Pho response via PhoP-PhoR. One pathway includes the ResD-ResE system, while the other involves a transition-state regulator, AbrB. The SpoO system represses the Pho response by negatively regulating both pathways. This review will discuss how the characterization of the APase multigene family made possible studies which show that the Pho regulon in B. subtilis is regulated by the integrated action of the Res, Pho and Spo signal-transduction systems.

The signal-transduction network for Pho regulation in Bacillus subtilis.

Genes from Bacillus subtilis predicted to encode a phosphate-specific transport (Pst) system were shown by mutation to affect high-affinity Pi uptake but not arsenate resistance or phosphate (Pho) regulation. The transcription start of the promoter upstream of the pstS gene was defined by primer extension. The promoter contains structural features analogous to the Escherichia coli pst promoter but not sequence similarity. Expression from this promoter was induced >5,000-fold upon phosphate starvation and regulated by the PhoP-PhoR two-component regulatory system. These data indicate that the pst operon is involved in phosphate transport and is a member of the Pho regulon but is not involved in Pi regulation.

The pst operon of Bacillus subtilis has a phosphate-regulated promoter and is involved in phosphate transport but not in regulation of the pho regulon.

The Bacillus subtilis pstS operon and phoA gene are members of the Pho regulon that is controlled by PhoR, a histidine kinase, and PhoP, a response regulator. Footprinting analysis showed that phosphorylated PhoP extended the PhoP protected region in pstS and phoA promoters, and also bound to a separate site within the coding region of each gene. Our previous in vivo studies have shown that, in contrast to other Pho regulon promoters that are not expressed in either phoP or phoR mutants, a low-level induction from the pstS promoter (25% of parent strain) can be detected in a phoR mutant. In this study, by using an in vitro transcription system, we demonstrate that (i) only phosphorylated PhoP is a transcriptional activator of the pstS operon and of the phoA gene; (ii) phosphorylated PhoP and RNA polymerase sigmaA holoenzyme are sufficient for in vitro transcription of the pstS promoter and the phoA promoter; (iii) the activation of the pstS promoter requires lower concentrations of phosphorylated PhoP than does the phoA promoter for transcription; and (iv) PhoP binding sites in both the pstS promoter core binding region and in the 5' coding region of the gene, which have been identified by footprinting analysis, are important for the transcription of the pstS promoter in vitro.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2958.1998.00882.x

PhoP-P and RNA polymerase sigmaA holoenzyme are sufficient for transcription of Pho regulon promoters in Bacillus subtilis: PhoP-P activator sites within the coding region stimulate transcription in vitro.

Bacillus subtilis alkaline phosphatases III and IV : cloning, sequencing, and comparisons of deduced amino acid sequence with Escherichia coli alkaline phosphatase three-dimensional structure

F M Hulett

Papers

Regulators of aerobic and anaerobic respiration in Bacillus subtilis.

The signal-transduction network for Pho regulation in Bacillus subtilis.

The pst operon of Bacillus subtilis has a phosphate-regulated promoter and is involved in phosphate transport but not in regulation of the pho regulon.

PhoP-P and RNA polymerase sigmaA holoenzyme are sufficient for transcription of Pho regulon promoters in Bacillus subtilis: PhoP-P activator sites within the coding region stimulate transcription in vitro.

Bacillus subtilis alkaline phosphatases III and IV : cloning, sequencing, and comparisons of deduced amino acid sequence with Escherichia coli alkaline phosphatase three-dimensional structure