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Structural-functional aspects of the Bordetella pertussis adenylate cyclase toxin
Březinová, Karolína ; Bumba, Ladislav (advisor) ; Brzobohatá, Hana (referee)
Whooping cough (pertussis) is a highly infectious respiratory disease caused by the Gram-negative bacterium Bordetella pertussis. Even though the vaccination rate of the population is high, pertussis is one of the most widespread vaccine-preventable diseases. The bacterium produces a variety of virulence factors that facilitate the process of colonization of the ciliated epithelium and infection of the upper respiratory tract. Among the most important virulence factors is the adenylate cyclase toxin (CyaA). This toxin belongs to the so- called RTX (Repeat-In-ToXins) proteins, which are released from the bacterium using the Type 1 secretion apparatus (T1SS). CyaA is a multifunctional toxin, showing both hemolytic and cytotoxic activity. The cytotoxic activity is caused by the N-terminal adenylyl cyclase (AC) domain, which is translocated across the cytoplasmic membrane into the cell cytosol, where upon interaction with calmodulin catalyzes the uncontrolled conversion of adenosine triphosphate (ATP) to cyclic adenosine-3',5'-monophosphate (cAMP). CyaA is recognized by the integrin receptor CD11b/CD18 (also known as complement receptor type 3), which is primarily found on phagocytic cells of the host organism. This work focuses on the structural- functional aspects of the CyaA toxin and summarizes...
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Conformation of the adenylate cyclase toxin of Bordetella pertussis.
Motlová, Lucia
This work is focused on the RTX (Repeats in ToXin) domains structure of selected RTX toxins and its impact on secretion and protein folding. The structural analysis included RTX domains of ApxI (Actinobacillus pleuropneumoniae-RTX-toxin I) from Actinobacillus pleuropneumoniae, HlyA (Alfa-hemolysin) from Escherichia coli and LtxA (Leukotoxin A) from Aggregatibacter actinomycetemcomitans and blocs 4 a 5 RTX domain CyaA (adenylate cyclase toxin) from Bordetella pertussis. The structures of LtxA RTX domain and CyaA RTX blocs 4 and 5 were obtained and characterized. Two models of CyaA RTX domain were built based on SAXS (Small Angle X-ray Scattering) model, previously solved RTX structures and RTX structures presented here.
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Mechanisms underlying subversion of host immunity by Bordetella pertussis
Klímová, Nela ; Bumba, Ladislav (advisor) ; Černý, Jan (referee) ; Filipp, Dominik (referee)
Bordetella pertussis is a Gram-negative human-adapted pathogen of the respiratory tract and the causative agent of the whooping cough (pertussis) illness. The bacterium produces a number of virulence factors, of which adenylate cyclase toxin (ACT) and pertussis toxin (PT) play important roles in manipulation of host immune response and establishment of the early catarrhal stage of infection. Although the toxins exert their cytotoxic activity by elevation of intracellular cAMP levels, both are distinct from each other in terms of their structures, mechanisms of secretion and cell intoxication, as well as in their ability to modulate the adaptive immune response of the host. The aim of this thesis was to determine the structure- function relationship underlying the mechanism of the Type I secretion system (T1SS)- mediated secretion of ACT and to decipher the immunomodulatory properties of ACT and PT in the course of B. pertussis infection. Integrative structural biology approaches revealed that the RTX domain of ACT consists of a contiguous assembly of five Ca2+ -loaded β-roll blocks, whose co-secretional folding constitute an intramolecular Brownian ratchet that prevents backsliding of the translocating polypeptide in the T1SS conduit, thus accelerating the secretion of ACT from bacterial cells by a...
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Preparation and characterization of protein constructs for structural analysis of acylate domain of adenylate cyclase toxin from bacteria B. pertussis
Ryvola, Vojtěch ; Ječmen, Tomáš (advisor) ; Chmelík, Josef (referee)
Whooping cough or pertussis is a contagious bacterial airways diasease caused by B. pertussis. Despite the high vaccination coverage of the population in developed countries, whooping cough is one of the most common diseases that can be prevented by vaccination. Bacteria B. pertussis produces a variety of toxins that facilitate the colonization and proliferation of bacterial cells in the host ciliary epithelium of the upper respiratory tract. One of these toxins is adenylate cyclase toxin, which is released from bacterial cells by a type I secretory apparatus and, after it's calcium-induced packaging, is able to transport its N-terminal adenylate cyclase domain across the cytoplasmic membrane of host cells. This domain able to catalyse conversion of adenosine triphosphate (ATP) to a cyclic adenosine monophosphate (cAMP) after the interaction with cytoplasmatic calmodulin. High levels of cAMP subsequently lead to impaired cell signaling and to a fundamental reduction in the bactericidal functions of phagocytic cells. The aim of this bachelor thesis was to prepare and characterize 'hybrid' protein constructs, which consist of a C-terminal part of the acylation domain and an N-terminal part of the RTX domain (at positions 881-1038 and 881-1047) linked to the C-terminal part of the RTX domain (at...
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The role of a conserved tyrosine residue of acylated domain in membrane insertion and penetration of RTX toxins
Lepesheva, Anna ; Mašín, Jiří (advisor) ; Petráčková, Denisa (referee)
Pore-forming RTX toxins are key virulence factors of many Gram-negative pathogens. These proteins share several common structural and functional features: (i) the presence of repetitive sequences rich in glycine and aspartate, which are important for calcium ion binding, (ii) transport from the bacterial cytosol through the type I secretion system (T1SS), (iii) modification by a fatty acid at specific lysines in the acylated domain by a specific acyltransferase, and (iv) the presence of an amphipathic region responsible for the formation of cation-selective pores in the target membrane. The aromatic side chain of the conserved tyrosine residue 940 in the acylated segment of the RTX adenylate cyclase toxin (CyaA, ACT or AC-Hly) of Bordetella pertussis plays a key role in the interaction of the toxin with the target cell membrane. The aim of this study was to determine whether the corresponding conserved residues Y940, Y642, Y643 and Y639 secreted by the homologous RTX toxin CyaA from Bordetella bronchiseptica, HlyA from Escherichia coli, ApxIA from Actinobacillus pleuropneumoniae and RtxA from Kingella kingae play the same critical role in membrane insertion and pore formation. The hemolytic and cytotoxic activities of these toxins were completely impaired only after replacement of the conserved...
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Immunomodulation of dendritic cells by adenylate cyclase toxin from B. pertussis
Jáňová, Hana ; Adkins, Irena (advisor) ; Brdička, Tomáš (referee)
Adenylate cyclase toxin (CyaA) produced by the causative agent of whooping cough Bordetella pertussis, is a key virulence factor important for colonization of the host. CyaA targets preferentially myeloid phagocytes expressing CD11b/CD18 integrin. By elevating cytosolic cAMP in the host cells, CyaA interferes with their phagocytic, chemotactic and oxidative burst capacities. Furthermore, CyaA modulates the secretion of cytokines and the maturation state in LPS-stimulated dendritic cells (DC) by affecting the expression of costimulatory molecules. In this study, we investigated the effects of CyaA on the capacity of murine bone-marrow DC to prime CD4+ and CD8+ T cells in response to ovalbumin epitopes delivered by the CyaA-AC- toxoid, as a model antigen. Further, we examined the possible impact of CyaA on the antigen uptake and processing for MHC class I and II-restricted presentation by DC, as we previously observed a decreased T cell stimulatory capacity of CyaA-treated DC in response to soluble ovalbumin. We found out that the high levels of cAMP generated by CyaA in LPS-stimulated DC account for the decreased presentation of ovalbumin epitopes carried by CyaA-AC- toxoid on MHC class I and II molecules, thereby impairing the CD8+ and CD4+ T cell responses. Whereas CyaA did not influence the...
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Adenylate cyclase toxin of Bordetella pertussis, its conformation and ion balance in host cell.
Motlová, Lucia ; Konopásek, Ivo (advisor) ; Krůšek, Jan (referee)
Adenylate cyclase (CyaA, ACT) toxin is one of the major virulence factors of Bordetella pertussis. Although CyaA binds to many types of membranes, it is assumed that the integrin CD11b/CD18 is its receptor which is expressed on the surface of myeloid cells. CyaA belongs to the family of RTX toxin-hemolysins. CyaA acts on the host cells by two independent activities. One of them is the conversion of ATP to cyclic AMP, which is catalyzed by adenylate cyclase (AC) domain after its translocation into the cytosol of the host cell, which leads to the entry of calcium cations into the host cell. Translocation is probably initiated by interaction of CyaA monomer with the target membrane. The second activity is the formation of CyaA channel selective for cations, which probably causes colloid osmotic lysis of target cells. The channel forming activity is provided by RTX hemolysin domain which most probably forms oligomers, although it was found that CyaA as a monomer causes leakage of potassium cations from the host cell. It is also not clear whether the oligomerization of CyaA would occur in solution, or after interaction with the host membrane. The aim of this study was to examine the flow of sodium ions on the membrane of murine macrophages J774A.1, which express integrin CD11b/CD18 on their surface....
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Construction and characterization of recombinant adenylate cyclase toxoid of bacterium Bordetella pertussis carrying mycobacterial antigen TB7.7
Mikulecký, Pavel ; Staněk, Ondřej (advisor) ; Vopálenský, Václav (referee)
Bacterium Mycobacterium tuberculosis is an etiological agent of a deadly disease called tuberculosis that presents a global problem. According to The World Health Organization there are more than 2 billions people infected with latent tuberculosis all over the world. There is still need of specific, sensitive, quick and economic available method for identification of infected individuals. Currently in vitro blood tests are considered to be the best way of diagnosis. They are based on restimulation of specific T lymphocytes by mycobacterial antigens derived from virulent strains. There are several different approaches for enhancing of direct antigen delivery into antigen presenting cells and promising one is a genetically detoxified adenylate cyclase toxin (CyaA) of bacteria Bordetella pertussis. The main aim of the thesis includes construction and subsequent characterization of biological properties of CyaA protein carrying specific mycobacterial antigen TB7.7 in translocating domain. Here is shown that fusion protein CyaA-TB7.7 can form cation selective pores in target cell membranes and is able to deliver antigens into the cytosol of APC to be presented on surface with molecules MHC class II. Genetically detoxified CyaA- TB7.7 protein will be used to supplement current approaches such as also in vitro...
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Signalization of adenylate cyclase toxin of Bordetella pertussis in macrophages.
Černý, Ondřej ; Kamanová, Jana (advisor) ; Kuthan, Martin (referee)
Adenylate cyclase toxin (CyaA) is a key virulence factor of Bordetella pertussis, the causative agent of whooping cough. The toxin targets primarily myeloid phagocytes expressing CD11b/CD18 (αMβ2, CR3, Mac-1) and by elevation of cytosolic cAMP levels it paralyses their macropinocytic and opsono-phagocytic functions. Here, we dissected the cAMP-regulated pathway responsible for the block of macrophage macropinocytosis and characterized the capacity of CyaA-treated macrophages to shut- down Akt (protein kinase B, PKB) signaling; that controls nitric oxide (NO) production by macrophages. By using specific activators of protein kinase A (PKA) and for the exchange protein activated by cAMP (Epac), we show that activation of the cAMP effector Epac inhibits macropinocytosis in macrophages. Moreover, upon transfection of macrophages by the constitutively active and dominant negative variants of a downstream effector of Epac, the small GTPase Rap1, inhibition or upregulation of macrophage macropinocytosis was observed, respectively. It was reported previously that the Epac/Rap1 pathway regulates activity of tyrosin phosphatase SHP-1 as well as of protein phosphatase 2 A (PP2A). We show that inhibition of both tyrosin phosphatases and PP2A interferes with CyaA-mediated block of macropinocytosis. These...
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The role of RTX domain in the activity of adenylate cyclase toxin from Bordetella pertussis
Klímová, Nela ; Bumba, Ladislav (advisor) ; Konopásek, Ivo (referee)
The adenylate cyclase toxin (CyaA) of Bordetella pertussis is a 1706-residue protein comprising an amino-terminal adenylate cyclase (AC) domain and a carboxy-terminal Repeat-in-Toxin (RTX) domain. The RTX domain is a hallmark of the family of RTX proteins, which are secreted from the cytosol of Gram-negative bacteria to the cell environment through the Type I Secretion System (T1SS). The RTX domain of CyaA consists of five blocks of RTX nonapetide repeats with a consensus sequence X-(L/I/V)-X-G-G-X-G- X-D. The aim of this work was to determine the role of the RTX domain in biological activities of CyaA and its role in the secretion of the toxin molecule from Bordetella pertussis. Systematic deletion analysis revealed that none of the prepared CyaA constructs was able to translocate its AC domain across the cytoplasmic membrane of host cells and make pores in target membranes. Moreover, deletion of individual RTX repeat blocks resulted in a very low efficacy of secretion of CyaA mutants into cell exterior. These data suggested that structural integrity of the RTX domain of CyaA is essential not only for cytotoxic activities of the toxin molecule but also for its secretion through the T1SS.
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