scholarly journals Alternate subunit assembly diversifies the function of a bacterial toxin

2019 ◽  
Author(s):  
Casey Fowler ◽  
Gabrielle Stack ◽  
Xuyao Jiao ◽  
Maria Lara-Tejero ◽  
Jorge E. Galán
Keyword(s):  
Virulence Factor ◽  
Structural Design ◽  
Laboratory Animals ◽  
Bacterial Toxin ◽  
New Paradigm ◽  
A Subunit ◽  
Functionally Diverse ◽  
Typhoid Toxin ◽  
Active Subunits ◽  
Functional Versatility

AbstractBacterial toxins with an AB5architecture are central to bacterial pathogenesis. Functionally diverse and evolutionarily distant AB5toxins adopt synonymous structures in which a discrete domain of the toxin’s active (A) subunit is inserted into a ring-like platform comprised of five delivery (B) subunits.SalmonellaTyphi, the cause of typhoid fever, produces an unusual A2B5toxin known as typhoid toxin, a major virulence factor. Here, we report that upon infection of human cells,S. Typhi produces two forms of typhoid toxin that have distinct delivery components but share common active subunits. We demonstrate that the two typhoid toxins exhibit substantially different trafficking properties, elicit markedly different effects when administered to laboratory animals, and are expressed in response to different regulatory mechanisms and distinct metabolic cues. Collectively, these results indicate that the evolution of two typhoid toxin variants has conferred functional versatility to this virulence factor. More broadly, this study reveals a new paradigm in toxin biology and suggests that the evolutionary expansion of AB5toxins was likely fueled by the remarkable plasticity inherent to their structural design coupled to the functional versatility afforded by the combination of homologous toxin components.

scholarly journals Characterization of C3larvinA, a novel RhoA-targeting ADP-ribosyltransferase toxin produced by the honey bee pathogen, Paenibacillus larvae

2020 ◽  
Vol 40 (1) ◽  
Author(s):  
Madison Turner ◽  
Olivier Tremblay ◽  
Kayla A. Heney ◽  
Miguel R. Lugo ◽  
Julia Ebeling ◽  
...  
Keyword(s):  
Virulence Factor ◽  
Catalytic Mechanism ◽  
Homology Model ◽  
Covalent Modification ◽  
Paenibacillus Larvae ◽  
Bacterial Toxin ◽  
Transferase Activity ◽  
Putative Virulence Factor ◽  
Cellular Effects ◽  
Biological Target

Abstract C3larvinA is a putative virulence factor produced by Paenibacillus larvae enterobacterial-repetitive-intergenic-consensus (ERIC) III/IV (strain 11-8051). Biochemical, functional and structural analyses of C3larvinA revealed that it belongs to the C3-like mono-ADP-ribosylating toxin subgroup. Mammalian RhoA was the target substrate for its transferase activity suggesting that it may be the biological target of C3larvinA. The kinetic parameters of the NAD+ substrate for the transferase (KM = 75 ± 10 µM) and glycohydrolase (GH) (KM = 107 ± 20 µM) reactions were typical for a C3-like bacterial toxin, including the Plx2A virulence factor from Paenibacillus larvae ERIC I. Upon cytoplasmic expression in yeast, C3larvinA caused a growth-defective phenotype indicating that it is an active C3-like toxin and is cytotoxic to eukaryotic cells. The catalytic variant of the Q187-X-E189 motif in C3larvinA showed no cytotoxicity toward yeast confirming that the cytotoxicity of this factor depends on its enzymatic activity. A homology consensus model of C3larvinA with NAD+ substrate was built on the structure of Plx2A, provided additional confirmation that C3larvinA is a member of the C3-like mono-ADP-ribosylating toxin subgroup. A homology model of C3larvinA with NADH and RhoA was built on the structure of the C3cer-NADH-RhoA complex which provided further evidence that C3larvinA is a C3-like toxin that shares an identical catalytic mechanism with C3cer from Bacillus cereus. C3larvinA induced actin cytoskeleton reorganization in murine macrophages, whereas in insect cells, vacuolization and bi-nucleated cells were observed. These cellular effects are consistent with C3larvinA disrupting RhoA function by covalent modification that is shared among C3-like bacterial toxins.

The structure of urease inactivated by Ag(i): a new paradigm for enzyme inhibition by heavy metals

2018 ◽  
Vol 47 (25) ◽  
pp. 8240-8247 ◽  
Author(s):  
Luca Mazzei ◽  
Michele Cianci ◽  
Antonio Gonzalez Vara ◽  
Stefano Ciurli
Keyword(s):  
Crystal Structure ◽  
Heavy Metals ◽  
Enzyme Inhibition ◽  
Virulence Factor ◽  
Soil Nitrogen ◽  
Nitrogen Fertilization ◽  
Enzyme Complex ◽  
Human Pathogens ◽  
New Paradigm

The molecular details of the inactivation of urease, a nickel-dependent virulence factor for human pathogens and negatively affecting the efficiency of soil nitrogen fertilization, are elucidated through the crystal structure of the enzyme complex with Ag(i).

scholarly journals The C. albicans virulence factor Candidalysin polymerizes in solution to form membrane pores and damage epithelial cells.

2021 ◽  
Author(s):  
Charles M Russell ◽  
Katherine Schaefer ◽  
Andrew Dixson ◽  
Amber Gray ◽  
Robert Jordan Pyron ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Molecular Mechanism ◽  
Virulence Factor ◽  
Cell Biology ◽  
Pathogenic Fungus ◽  
Cellular Damage ◽  
Linear Polymers ◽  
Biophysical Modeling ◽  
New Paradigm ◽  
Membrane Pores

The pathogenic fungus Candida albicans causes severe invasive candidiasis. C. albicans infection requires the action of the virulence factor Candidalysin (CL), which damages the plasma membrane of the target human cells. However, the molecular mechanism that CL uses to permeabilize membranes is poorly understood. We employed complementary biophysical, modeling, microscopy, and cell biology methods to reveal that CL forms membrane pores using a unique molecular mechanism. Unexpectedly, it was observed that CL readily assembles into linear polymers in solution. The basic structural unit in polymer formation is a CL 8-mer, which is sequentially added into a string configuration. Finally, the linear polymers can close into a loop. Our data indicate that CL loops spontaneously insert into the membrane to become membrane pores. We identified a CL mutation (G4W) that inhibited the formation of polymers in solution and prevented formation of pores in different synthetic lipid membranes systems. Studies in epithelial cells showed that G4W CL failed to activate the danger response signaling pathway, a hallmark of the pathogenic effect of CL. These results indicate that CL polymerization in solution is a necessary step for the damage of cellular membranes. Analysis of thousands of CL pores by atomic force microscopy revealed the co existence of simple depressions and complex pores decorated with protrusions. Imaging and modeling indicate that the two types of pores are formed by CL molecules assembled into alternate orientations. We propose that this structural rearrangement represents a maturation mechanism that might stabilize pore formation to achieve more robust cellular damage. Taken together, the data show that CL uses a previously unknown mechanism to damage membranes, whereby pre-assembly of CL loops in solution directly leads to formation of membrane pores. Our investigation not only unravels a new paradigm for the formation of membrane pores, but additionally identifies CL polymerization as a novel therapeutic target to treat candidiasis.

scholarly journals A New Family of Potent AB5 Cytotoxins Produced by Shiga Toxigenic Escherichia coli

2004 ◽  
Vol 200 (1) ◽  
pp. 35-46 ◽  
Author(s):  
Adrienne W. Paton ◽  
Potjanee Srimanote ◽  
Ursula M. Talbot ◽  
Hui Wang ◽  
James C. Paton
Keyword(s):  
Escherichia Coli ◽  
Bacterial Toxin ◽  
Virulence Plasmid ◽  
B Subunit ◽  
New Family ◽  
Uremic Syndrome ◽  
A Subunit ◽  
K 12 ◽  
Ab5 Toxins ◽  
Subtilase Cytotoxin

The Shiga toxigenic Escherichia coli (STEC) O113:H21 strain 98NK2, which was responsible for an outbreak of hemolytic uremic syndrome, secretes a highly potent and lethal subtilase cytotoxin that is unrelated to any bacterial toxin described to date. It is the prototype of a new family of AB5 toxins, comprising a single 35-kilodalton (kD) A subunit and a pentamer of 13-kD B subunits. The A subunit is a subtilase-like serine protease distantly related to the BA_2875 gene product of Bacillus anthracis. The B subunit is related to a putative exported protein from Yersinia pestis, and binds to a mimic of the ganglioside GM2. Subtilase cytotoxin is encoded by two closely linked, cotranscribed genes (subA and subB), which, in strain 98NK2, are located on a large, conjugative virulence plasmid. Homologues of the genes are present in 32 out of 68 other STEC strains tested. Intraperitoneal injection of purified subtilase cytotoxin was fatal for mice and resulted in extensive microvascular thrombosis, as well as necrosis in the brain, kidneys, and liver. Oral challenge of mice with E. coli K-12–expressing cloned subA and subB resulted in dramatic weight loss. These findings suggest that the toxin may contribute to the pathogenesis of human disease.

scholarly journals Innate Lymphoid Cell–Dependent Airway Epithelial and Inflammatory Responses to Inhaled Ozone: A New Paradigm in Pathogenesis

2019 ◽  
Vol 47 (8) ◽  
pp. 993-1003 ◽  
Author(s):  
Jack R. Harkema ◽  
James G. Wagner
Keyword(s):  
Inflammatory Responses ◽  
Mucous Cell ◽  
Upper Airway ◽  
Air Pollutant ◽  
Lymphoid Cells ◽  
Laboratory Animals ◽  
New Paradigm ◽  
Type 2 Immunity ◽  
Airway Pathology

Epidemiological associations have been made between the new onset of childhood rhinitis/asthma and exposures to elevated ambient levels of ozone, a commonly encountered gaseous air pollutant. Our laboratory was the first to find that mice repeatedly exposed to ozone develop nasal type 2 immunity and eosinophilic rhinitis with mucous cell metaplasia. More recently, we have found that these ozone-induced upper airway alterations are mediated by group 2 innate lymphoid cells (ILC2s) and not by T and B cells that are important in adaptive immune responses typically associated with allergic rhinitis and asthma. Furthermore, repeated exposures of mice to ozone cause ILC2-mediated type 2 immunity and airway pathology in the lungs, like those found in the nasal airways. Our recent findings in ozone-exposed mice complement and extend previous reports of nonallergic nasal airway disease in ozone-exposed rats and nonhuman primates. Overall, these experimental results in laboratory animals suggest a plausible ILC2-dependent paradigm for the toxicologic pathobiology that underlies the development of nonallergic rhinitis/asthma in children who live in environments with repeated occurrences of high ambient concentrations of ozone.

scholarly journals SUMO E3 ligase Mms21 prevents spontaneous DNA damage induced genome rearrangements

2017 ◽  
Author(s):  
Jason Liang ◽  
Bin-zhong Li ◽  
Alexander P. Tan ◽  
Richard D. Kolodner ◽  
Christopher D. Putnam ◽  
...  
Keyword(s):  
Dna Damage ◽  
E3 Ligase ◽  
Genome Rearrangements ◽  
Dna Helicase ◽  
Dna Lesions ◽  
Genome Maintenance ◽  
New Paradigm ◽  
A Subunit ◽  
Sumo E3 Ligase ◽  
Break Induced Replication

AbstractMms21, a subunit of the Smc5/6 complex, possesses an E3 ligase activity for the Small Ubiquitin-like MOdifier (SUMO), which has a major, but poorly understood role in genome maintenance. Here we show mutations that inactivate the E3 ligase activity of Mms21 cause Rad52- and Pol32-dependent break-induced replication (BIR), which specifically requires the Rrm3 DNA helicase. Interestingly, mutations affecting both Mms21 and the Sgs1 helicase, but not sumoylation of Sgs1, cause further accumulation of genome rearrangements, indicating the distinct roles of Mms21 and Sgs1 in suppressing genome rearrangements. Whole genome sequencing further revealed that the Mre11 endonuclease prevents microhomology-mediated translocations and hairpin-mediated inverted duplications in the mms21 mutant. Consistent with the accumulation of endogenous DNA lesions, mms21 cells accumulate spontaneous Ddc2 foci and display a hyper-activated DNA damage checkpoint. Together, these findings support a new paradigm that Mms21 prevents the accumulation of spontaneous DNA lesions that cause diverse genome rearrangements.

scholarly journals Form Follows Availability – Designing Structures Through Reuse

2019 ◽  
Vol 60 (4) ◽  
pp. 257-265 ◽  
Author(s):  
Jan Brütting ◽  
Gennaro Senatore ◽  
Corentin Fivet
Keyword(s):  
Structural Design ◽  
Minimum Weight ◽  
Major Influence ◽  
Building Structures ◽  
Structural Elements ◽  
New Paradigm ◽  
New Material ◽  
Section Type ◽  
Minimum Weight Structures ◽  
Structure Layout

This work proposes a new direction in structural design: the synthesis of structures through the reuse of elements. Reusing structural elements reduces the environmental impacts of building structures because it avoids sourcing new material, it reduces waste and it requires little energy. Designing structures from reused elements is unlike conventional structural design because stock element availability is a design input. In other words, structures must be designed subject to availability of given element characteristics such as length and cross-section type, which have a major influence on the optimal structure layout and form. In this new paradigm structural form follows availability. In this work new computational methods for the synthesis of reticular structures through reuse are formulated to address two scenarios: a) reuse of reclaimed elements from a given stock, and b) design of an element stock which is used as a kit of parts to build diverse structures. Case studies are presented to demonstrate the potential of the proposed methods. It is shown that structures produced by these methods have a significantly lower environmental impact than minimum weight structures made of new elements.

Solar Filaments as Tracers of Subsurface Processes

2000 ◽  
Vol 179 ◽  
pp. 177-183
Author(s):  
D. M. Rust
Keyword(s):  
Magnetic Fields ◽  
Magnetic Flux ◽  
Coronal Mass Ejections ◽  
Interplanetary Space ◽  
Intermediate Stage ◽  
Coronal Plasma ◽  
Magnetic Helicity ◽  
The Sun ◽  
New Paradigm ◽  
Solar Filaments

AbstractSolar filaments are discussed in terms of two contrasting paradigms. The standard paradigm is that filaments are formed by condensation of coronal plasma into magnetic fields that are twisted or dimpled as a consequence of motions of the fields’ sources in the photosphere. According to a new paradigm, filaments form in rising, twisted flux ropes and are a necessary intermediate stage in the transfer to interplanetary space of dynamo-generated magnetic flux. It is argued that the accumulation of magnetic helicity in filaments and their coronal surroundings leads to filament eruptions and coronal mass ejections. These ejections relieve the Sun of the flux generated by the dynamo and make way for the flux of the next cycle.

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