Vibrio cholerae NspS, a homologue of ABC-type periplasmic solute binding proteins, facilitates transduction of polyamine signals independent of their transport

The polyamines norspermidine and spermidine are among the environmental signals that regulate Vibrio cholerae biofilm formation. The effects of these polyamines are mediated by NspS, a member of the bacterial periplasmic solute binding protein superfamily. Almost all members of this superfamily characterized to date are components of ATP-binding cassette-type transporters involved in nutrient uptake. Consequently, in the current annotation of the V. cholerae genome, NspS has been assigned a function in transport. The objective of this study was to further characterize NspS and investigate its potential role in transport. Our results support a role for NspS in signal transduction in response to norspermidine and spermidine, but not their transport. In addition, we provide evidence that these polyamine signals are processed by c-di-GMP signalling networks in the cell. Furthermore, we present comparative genomics analyses which reveal the presence of NspS-like proteins in a variety of bacteria, suggesting that periplasmic ligand binding proteins may be widely utilized for sensory transduction.

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A mutagenic screen reveals NspS residues important for regulation of Vibrio cholerae biofilm formation

Microbiology ◽

10.1099/mic.0.001023 ◽

2021 ◽

Author(s):

Erin C. Young ◽

Jackson T. Baumgartner ◽

Ece Karatan ◽

Misty L. Kuhn

Keyword(s):

Signal Transduction ◽

Ligand Binding ◽

Vibrio Cholerae ◽

Biofilm Formation ◽

Type Species ◽

Binding Proteins ◽

Signal Transduction Pathway ◽

Signalling Pathway ◽

Content Type ◽

Link Type

Biofilm formation in the human intestinal pathogen Vibrio cholerae is in part regulated by norspermidine, spermidine and spermine. V. cholerae senses these polyamines through a signalling pathway consisting of the periplasmic protein, NspS, and the integral membrane c-di-GMP phosphodiesterase MbaA. NspS and MbaA belong to a proposed class of novel signalling systems composed of periplasmic ligand-binding proteins and membrane-bound c-di-GMP phosphodiesterases containing both GGDEF and EAL domains. In this signal transduction pathway, NspS is hypothesized to interact with MbaA in the periplasm to regulate its phosphodiesterase activity. Polyamine binding to NspS likely alters this interaction, leading to the activation or inhibition of biofilm formation depending on the polyamine. The purpose of this study was to determine the amino acids important for NspS function. We performed random mutagenesis of the nspS gene, identified mutant clones deficient in biofilm formation, determined their responsiveness to norspermidine and mapped the location of these residues onto NspS homology models. Single mutants clustered on two lobes of the NspS model, but the majority were found on a single lobe that appeared to be more mobile upon norspermidine binding. We also identified residues in the putative ligand-binding site that may be important for norspermidine binding and interactions with MbaA. Ultimately, our results provide new insights into this novel signalling pathway in V. cholerae and highlight differences between periplasmic binding proteins involved in transport versus signal transduction.

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The Two-Component Signal Transduction System VxrAB Positively Regulates Vibrio cholerae Biofilm Formation

Journal of Bacteriology ◽

10.1128/jb.00139-17 ◽

2017 ◽

Vol 199 (18) ◽

Cited By ~ 15

Author(s):

Jennifer K. Teschler ◽

Andrew T. Cheng ◽

Fitnat H. Yildiz

Keyword(s):

Signal Transduction ◽

Vibrio Cholerae ◽

Histidine Kinase ◽

Biofilm Formation ◽

Pathogenic Bacteria ◽

Response Regulator ◽

Systematic Analysis ◽

Content Type ◽

Two Component ◽

Two Component Signal Transduction

ABSTRACT Two-component signal transduction systems (TCSs), typically composed of a sensor histidine kinase (HK) and a response regulator (RR), are the primary mechanism by which pathogenic bacteria sense and respond to extracellular signals. The pathogenic bacterium Vibrio cholerae is no exception and harbors 52 RR genes. Using in-frame deletion mutants of each RR gene, we performed a systematic analysis of their role in V. cholerae biofilm formation. We determined that 7 RRs impacted the expression of an essential biofilm gene and found that the recently characterized RR, VxrB, regulates the expression of key structural and regulatory biofilm genes in V. cholerae. vxrB is part of a 5-gene operon, which contains the cognate HK vxrA and three genes of unknown function. Strains carrying ΔvxrA and ΔvxrB mutations are deficient in biofilm formation, while the ΔvxrC mutation enhances biofilm formation. The overexpression of VxrB led to a decrease in motility. We also observed a small but reproducible effect of the absence of VxrB on the levels of cyclic di-GMP (c-di-GMP). Our work reveals a new function for the Vxr TCS as a regulator of biofilm formation and suggests that this regulation may act through key biofilm regulators and the modulation of cellular c-di-GMP levels. IMPORTANCE Biofilms play an important role in the Vibrio cholerae life cycle, providing protection from environmental stresses and contributing to the transmission of V. cholerae to the human host. V. cholerae can utilize two-component systems (TCS), composed of a histidine kinase (HK) and a response regulator (RR), to regulate biofilm formation in response to external cues. We performed a systematic analysis of V. cholerae RRs and identified a new regulator of biofilm formation, VxrB. We demonstrated that the VxrAB TCS is essential for robust biofilm formation and that this system may regulate biofilm formation via its regulation of key biofilm regulators and cyclic di-GMP levels. This research furthers our understanding of the role that TCSs play in the regulation of V. cholerae biofilm formation.

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Identification of signaling pathways, matrix-digestion enzymes, and motility components controlling Vibrio cholerae biofilm dispersal

10.1101/2020.10.09.333351 ◽

2020 ◽

Author(s):

Andrew A. Bridges ◽

Chenyi Fei ◽

Bonnie L. Bassler

Keyword(s):

Signal Transduction ◽

Vibrio Cholerae ◽

Disease Transmission ◽

Biofilm Formation ◽

Cell Attachment ◽

Sensory System ◽

Matrix Degradation ◽

Free Swimming ◽

Molecular Events ◽

Biofilm Dispersal

AbstractBacteria alternate between being free-swimming and existing as members of sessile multicellular communities called biofilms. The biofilm lifecycle occurs in three stages: cell attachment, biofilm maturation, and biofilm dispersal. Vibrio cholerae biofilms are hyper-infectious and biofilm formation and dispersal are considered central to disease transmission. While biofilm formation is well-studied, almost nothing is known about biofilm dispersal. Here, we conduct an imaging screen for V. cholerae mutants that fail to disperse, revealing three classes of dispersal components: signal transduction proteins, matrix-degradation enzymes, and motility factors. Signaling proteins dominated the screen and among them, we focused on an uncharacterized two-component sensory system that we name DbfS/DbfR for Dispersal of Biofilm Sensor/Regulator. Phospho-DbfR represses biofilm dispersal. DbfS dephosphorylates and thereby inactivates DbfR, which permits dispersal. Matrix degradation requires two enzymes: LapG, which cleaves adhesins, and RbmB, which digests matrix polysaccharide. Reorientations in swimming direction, mediated by CheY3, are necessary for cells to escape from the porous biofilm matrix. We suggest that these components act sequentially: signaling launches dispersal by terminating matrix production and triggering matrix digestion and, subsequently, cell motility permits escape from biofilms. This study lays the groundwork for interventions that modulate V. cholerae biofilm dispersal to ameliorate disease.Significance statementThe pathogen Vibrio cholerae alternates between the free-swimming state and existing in sessile multicellular communities known as biofilms. Transitioning between these lifestyles is key for disease transmission. V. cholerae biofilm formation is well studied, however, almost nothing is known about how V. cholerae cells disperse from biofilms, precluding understanding of a central pathogenicity step. Here, we conducted a high-content imaging screen for V. cholerae mutants that failed to disperse. Our screen revealed three classes of components required for dispersal: signal transduction, matrix degradation, and motility factors. We characterized these components to reveal the sequence of molecular events that choreograph V. cholerae biofilm dispersal. Our report provides a framework for developing strategies to modulate biofilm dispersal to prevent or treat disease.

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Annexins - calcium- and membrane-binding proteins in the plant kingdom: potential role in nodulation and mycorrhization in Medicago truncatula.

Acta Biochimica Polonica ◽

10.18388/abp.2009_2451 ◽

2009 ◽

Vol 56 (2) ◽

Cited By ~ 26

Author(s):

Tanuja Talukdar ◽

Karolina Maria Gorecka ◽

Fernanda De Carvalho-Niebel ◽

J Allan Downie ◽

Julie Cullimore ◽

...

Keyword(s):

Signal Transduction ◽

Medicago Truncatula ◽

Binding Proteins ◽

Potential Role ◽

Mycorrhizal Fungus ◽

Calcium Signal ◽

Dependent Manner ◽

Calcium Response ◽

Nod Factor

Annexins belong to a family of multi-functional membrane- and Ca(2+)-binding proteins. The characteristic feature of these proteins is that they can bind membrane phospholipids in a reversible, Ca(2+)-dependent manner. While animal annexins have been known for a long time and are fairly well characterized, their plant counterparts were discovered only in 1989, in tomato, and have not been thoroughly studied yet. In the present review, we discuss the available information about plant annexins with special emphasis on biochemical and functional properties of some of them. In addition, we propose a link between annexins and symbiosis and Nod factor signal transduction in the legume plant, Medicago truncatula. A specific calcium response, calcium spiking, is an essential component of the Nod factor signal transduction pathway in legume plants. The potential role of annexins in the generation and propagation of this calcium signal is considered in this review. M. truncatula annexin 1 (MtAnn1) is a typical member of the plant annexin family, structurally similar to other members of the family. Expression of the MtAnn1 gene is specifically induced during symbiotic associations with both Sinorhizobium meliloti and the mycorrhizal fungus Glomus intraradices. Furthermore, it has been reported that the MtAnn1 protein is preferentially localized at the nuclear periphery of rhizobial-activated cortical cells, suggesting a possible role of this annexin in the calcium response signal elicited by symbiotic signals from rhizobia and mycorrhizal fungi.

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Sensor Domain of Histidine Kinase VxrA of Vibrio cholerae- A Hairpin-swapped Dimer and its Conformational Change

Journal of Bacteriology ◽

10.1128/jb.00643-20 ◽

2021 ◽

Author(s):

Kemin Tan ◽

Jennifer K. Teschler ◽

Ruiying Wu ◽

Robert P. Jedrzejczak ◽

Min Zhou ◽

...

Keyword(s):

Signal Transduction ◽

Cell Wall ◽

Vibrio Cholerae ◽

Conformational Change ◽

Histidine Kinase ◽

Biofilm Formation ◽

Environmental Changes ◽

Secretion System ◽

Regulation Mechanism ◽

Two Component

VxrA and VxrB are cognate histidine kinase (HK) - response regulator (RR) pairs of a two-component signaling system (TCS) found in Vibrio cholerae, a bacterial pathogen that causes cholera. The VxrAB TCS positively regulates virulence, the Type VI Secretion System, biofilm formation, and cell wall homeostasis in V. cholerae, providing protection from environmental stresses and contributing to the transmission and virulence of the pathogen. The VxrA HK has a unique periplasmic sensor domain (SD) and, remarkably, lacks a cytoplasmic linker domain between the second transmembrane helix and the dimerization and histidine phosphotransfer (DHp) domain, indicating that this system may utilize a potentially unique signal sensing and transmission TCS mechanism. In this study, we have determined several crystal structures of VxrA-SD and its mutants. These structures reveal a novel structural fold forming an unusual β hairpin-swapped dimer. A conformational change caused by relative rotation of the two monomers in a VxrA-SD dimer could potentially change the association of transmembrane helices and, subsequently, the pairing of cytoplasmic DHp domains. Based on the structural observation, we propose a putative scissor-like closing regulation mechanism for the VxrA HK. IMPORTANCE V. cholerae has a dynamic life cycle, which requires rapid adaptation to changing external conditions. Two-component signal transduction (TCS) systems allow V. cholerae to sense and respond to these environmental changes. The VxrAB TCS positively regulates a number of important V. cholerae phenotypes, including virulence, the Type Six Secretion System, biofilm formation, and cell wall homeostasis. Here, we provide the crystal structure of the VxrA sensor histidine kinase sensing domain and propose a mechanism for signal transduction. The cognate signal for VxrAB remains unknown, however, in this work we couple our structural analysis with functional assessments of key residues to further our understanding of this important TCS.

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