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Ul Mushtaq, A., Ådén, J., Alam, A., Sjöstedt, A. & Gröbner, G. (2022). Backbone chemical shift assignment and dynamics of the N-terminal domain of ClpB from Francisella tularensis type VI secretion system. Biomolecular NMR Assignments, 16, 75-79
Open this publication in new window or tab >>Backbone chemical shift assignment and dynamics of the N-terminal domain of ClpB from Francisella tularensis type VI secretion system
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2022 (English)In: Biomolecular NMR Assignments, ISSN 1874-2718, E-ISSN 1874-270X, Vol. 16, p. 75-79Article in journal (Refereed) Published
Abstract [en]

The Hsp100 family member ClpB is a protein disaggregase which solubilizes and reactivates stress-induced protein aggregates in cooperation with the DnaK/Hsp70 chaperone system. In the pathogenic bacterium Francisella tularensis, ClpB is involved in type VI secretion system (T6SS) disassembly through depolymerization of the IglA-IglB sheath. This leads to recycling and reassembly of T6SS components and this process is essential for the virulence of the bacterium. Here we report the backbone chemical shift assignments and 15N relaxation-based backbone dynamics of the N-terminal substrate-binding domain of ClpB (1-156).

Place, publisher, year, edition, pages
Springer, 2022
Keywords
15N relaxation, ClpB chaperone, Francisella tularensis, NMR resonance assignment, Type VI secretion system
National Category
Structural Biology
Identifiers
urn:nbn:se:umu:diva-191275 (URN)10.1007/s12104-021-10062-3 (DOI)000739320300001 ()34985724 (PubMedID)2-s2.0-85122286521 (Scopus ID)
Funder
Swedish Research CouncilSwedish Cancer SocietyThe Kempe FoundationsKnut and Alice Wallenberg Foundation
Available from: 2022-01-13 Created: 2022-01-13 Last updated: 2023-03-24Bibliographically approved
Nadeem, A., Berg, A., Pace, H., Alam, A., Toh, E., Ådén, J., . . . Wai, S. N. (2022). Protein-lipid interaction at low pH induces oligomerization of the MakA cytotoxin from Vibrio cholerae. eLIFE, 11, Article ID e73439.
Open this publication in new window or tab >>Protein-lipid interaction at low pH induces oligomerization of the MakA cytotoxin from Vibrio cholerae
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2022 (English)In: eLIFE, E-ISSN 2050-084X, Vol. 11, article id e73439Article in journal (Refereed) Published
Abstract [en]

The α-pore-forming toxins (α-PFTs) from pathogenic bacteria damage host cell membranes by pore formation. We demonstrate a remarkable, hitherto unknown mechanism by an α-PFT protein from Vibrio cholerae. As part of the MakA/B/E tripartite toxin, MakA is involved in membrane pore formation similar to other α-PFTs. In contrast, MakA in isolation induces tube-like structures in acidic endosomal compartments of epithelial cells in vitro. The present study unravels the dynamics of tubular growth, which occurs in a pH-, lipid-, and concentration-dependent manner. Within acidified organelle lumens or when incubated with cells in acidic media, MakA forms oligomers and remodels membranes into high-curvature tubes leading to loss of membrane integrity. A 3.7 Å cryo-electron microscopy structure of MakA filaments reveals a unique protein-lipid superstructure. MakA forms a pinecone-like spiral with a central cavity and a thin annular lipid bilayer embedded between the MakA transmembrane helices in its active α-PFT conformation. Our study provides insights into a novel tubulation mechanism of an α-PFT protein and a new mode of action by a secreted bacterial toxin.

Place, publisher, year, edition, pages
eLife Sciences Publications, Ltd, 2022
Keywords
Vibrio cholerae, MakA, lipid
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-192300 (URN)10.7554/eLife.73439 (DOI)2-s2.0-85124321786 (Scopus ID)
Funder
Swedish Research Council, 2018–02914Swedish Research Council, 2016–05009Swedish Research Council, 2019–01720Swedish Research Council, 2016–06963Swedish Research Council, 2019–02011Swedish Cancer Society, 2017–419Swedish Cancer Society, 2020–711The Kempe Foundations, JCK-1728The Kempe Foundations, SMK-1756.2The Kempe Foundations, SMK-1553The Kempe Foundations, JCK-1724The Kempe Foundations, SMK-1961Knut and Alice Wallenberg FoundationFamiljen Erling-Perssons Stiftelse
Available from: 2022-02-08 Created: 2022-02-08 Last updated: 2024-01-12Bibliographically approved
Nadeem, A., Nagampalli, R., Toh, E., Alam, A., Myint, S. L., Heidler, T., . . . Persson, K. (2021). A tripartite cytolytic toxin formed by Vibrio cholerae proteins with flagellum-facilitated secretion. Proceedings of the National Academy of Sciences of the United States of America, 118(47), Article ID e2111418118.
Open this publication in new window or tab >>A tripartite cytolytic toxin formed by Vibrio cholerae proteins with flagellum-facilitated secretion
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2021 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 118, no 47, article id e2111418118Article in journal (Refereed) Published
Abstract [en]

Vibrio cholerae, responsible for outbreaks of cholera disease, is a highly motile organism by virtue of a single flagellum. We describe how the flagellum facilitates the secretion of three V. cholerae proteins encoded by a hitherto-unrecognized genomic island. The proteins MakA/B/E can form a tripartite toxin that lyses erythrocytes and is cytotoxic to cultured human cells. A structural basis for the cytolytic activity of the Mak proteins was obtained by X-ray crystallography. Flagellum-facilitated secretion ensuring spatially coordinated delivery of Mak proteins revealed a role for the V. cholerae flagellum considered of particular significance for the bacterial environmental persistence. Our findings will pave the way for the development of diagnostics and therapeutic strategies against pathogenic Vibrionaceae.

National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:umu:diva-191257 (URN)10.1073/pnas.2111418118 (DOI)000727697700014 ()34799450 (PubMedID)2-s2.0-85121209218 (Scopus ID)
Funder
Swedish Research Council, 2016-05009Swedish Research Council, 2018-02914Swedish Research Council, 2019-01720Swedish Research Council, 2007-08673The Kempe Foundations, SMK-1756.2The Kempe Foundations, SMK-1553The Kempe Foundations, JCK-1728Swedish Cancer Society, 2017-419The Kempe Foundations, SMK-1961Swedish Research Council
Available from: 2022-01-12 Created: 2022-01-12 Last updated: 2023-05-11Bibliographically approved
Nadeem, A., Alam, A., Toh, E., Myint, S. L., Ur Rehman, Z., Liu, T., . . . Wai, S. N. (2021). Phosphatidic acid-mediated binding and mammalian cell internalization of the Vibrio cholerae cytotoxin MakA. PLoS Pathogens, 17(3), Article ID 1009414.
Open this publication in new window or tab >>Phosphatidic acid-mediated binding and mammalian cell internalization of the Vibrio cholerae cytotoxin MakA
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2021 (English)In: PLoS Pathogens, ISSN 1553-7366, E-ISSN 1553-7374, Vol. 17, no 3, article id 1009414Article in journal (Refereed) Published
Abstract [en]

Vibrio cholerae is a noninvasive intestinal pathogen extensively studied as the causative agent of the human disease cholera. Our recent work identified MakA as a potent virulence factor of V. cholerae in both Caenorhabditis elegans and zebrafish, prompting us to investigate the potential contribution of MakA to pathogenesis also in mammalian hosts. In this study, we demonstrate that the MakA protein could induce autophagy and cytotoxicity of target cells. In addition, we observed that phosphatidic acid (PA)-mediated MakA-binding to the host cell plasma membranes promoted macropinocytosis resulting in the formation of an endomembrane-rich aggregate and vacuolation in intoxicated cells that lead to induction of autophagy and dysfunction of intracellular organelles. Moreover, we functionally characterized the molecular basis of the MakA interaction with PA and identified that the N-terminal domain of MakA is required for its binding to PA and thereby for cell toxicity. Furthermore, we observed that the ΔmakA mutant outcompeted the wild-type V. cholerae strain A1552 in the adult mouse infection model. Based on the findings revealing mechanistic insights into the dynamic process of MakA-induced autophagy and cytotoxicity we discuss the potential role played by the MakA protein during late stages of cholera infection as an anti-colonization factor.

Place, publisher, year, edition, pages
Public Library of Science, 2021
National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-181991 (URN)10.1371/journal.ppat.1009414 (DOI)000631027700007 ()33735319 (PubMedID)2-s2.0-85103129339 (Scopus ID)
Available from: 2021-04-12 Created: 2021-04-12 Last updated: 2023-05-11Bibliographically approved
Nadeem, A., Aung, K. M., Ray, T., Alam, A., Persson, K., Pal, A., . . . Wai, S. N. (2021). Suppression of β-catenin signaling in colon carcinoma cells by a bacterial protein. International Journal of Cancer, 149(2), 442-459
Open this publication in new window or tab >>Suppression of β-catenin signaling in colon carcinoma cells by a bacterial protein
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2021 (English)In: International Journal of Cancer, ISSN 0020-7136, E-ISSN 1097-0215, Vol. 149, no 2, p. 442-459Article in journal (Refereed) Published
Abstract [en]

Colorectal cancer is one of the leading causes of cancer-related death worldwide. The adenomatous polyposis coli (APC) gene is mutated in hereditary colorectal tumors and in more than 80% of sporadic colorectal tumors. APC mutations impair β-catenin degradation, leading to its permanent stabilization and increased transcription of cancer-driving target genes. In colon cancer, impairment of β-catenin degradation leads to its cytoplasmic accumulation, nuclear translocation, and subsequent activation of tumor cell proliferation. Suppressing β-catenin signaling in cancer cells therefore appears to be a promising strategy for new anticancer strategies. Recently, we discovered a novel Vibrio cholerae cytotoxin, motility-associated killing factor A (MakA), that affects both invertebrate and vertebrate hosts. It promotes bacterial survival and proliferation in invertebrate predators but has unknown biological role(s) in mammalian hosts. Here, we report that MakA can cause lethality of tumor cells via induction of apoptosis. Interestingly, MakA exhibited potent cytotoxic activity, in particular against several tested cancer cell lines, while appearing less toxic toward nontransformed cells. MakA bound to the tumor cell surface became internalized into the endolysosomal compartment and induced leakage of endolysosomal membranes, causing cytosolic release of cathepsins and activation of proapoptotic proteins. In addition, MakA altered β-catenin integrity in colon cancer cells, partly through a caspase- and proteasome-dependent mechanism. Importantly, MakA inhibited β-catenin-mediated tumor cell proliferation. Remarkably, intratumor injection of MakA significantly reduced tumor development in a colon cancer murine solid tumor model. These data identify MakA as a novel candidate to be considered in new strategies for development of therapeutic agents against colon cancer.

Place, publisher, year, edition, pages
John Wiley & Sons, 2021
Keywords
apoptosis, cancer, lysosomes, MakA, proliferation, β-catenin
National Category
Cell and Molecular Biology Cancer and Oncology
Identifiers
urn:nbn:se:umu:diva-182176 (URN)10.1002/ijc.33562 (DOI)000632966400001 ()33720402 (PubMedID)2-s2.0-85103225384 (Scopus ID)
Funder
Swedish Cancer Society, 2017-419The Kempe Foundations, JCK-1728Swedish Research Council, 2007-08673, 2016-00968
Available from: 2021-04-15 Created: 2021-04-15 Last updated: 2021-07-13Bibliographically approved
Alam, A., Bröms, J. E., Kumar, R. & Sjöstedt, A. (2021). The Role of ClpB in Bacterial Stress Responses and Virulence. Frontiers in Molecular Biosciences, 8, Article ID 668910.
Open this publication in new window or tab >>The Role of ClpB in Bacterial Stress Responses and Virulence
2021 (English)In: Frontiers in Molecular Biosciences, E-ISSN 2296-889X, Vol. 8, article id 668910Article, review/survey (Refereed) Published
Abstract [en]

Bacterial survival within a mammalian host is contingent upon sensing environmental perturbations and initiating an appropriate counter-response. To achieve this, sophisticated molecular machineries are used, where bacterial chaperone systems play key roles. The chaperones are a prerequisite for bacterial survival during normal physiological conditions as well as under stressful situations, e.g., infection or inflammation. Specific stress factors include, but are not limited to, high temperature, osmolarity, pH, reactive oxidative species, or bactericidal molecules. ClpB, a member of class 1 AAA+ proteins, is a key chaperone that via its disaggregase activity plays a crucial role for bacterial survival under various forms of stress, in particular heat shock. Recently, it has been reported that ClpB also regulates secretion of bacterial effector molecules related to type VI secretion systems. In this review, the roles of ClpB in stress responses and the mechanisms by which it promotes survival of pathogenic bacteria are discussed.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2021
Keywords
ClpB chaperone, ClpB inhibitor, heat shock, stress response, type VI secretion
National Category
Microbiology in the medical area Cell and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-183530 (URN)10.3389/fmolb.2021.668910 (DOI)000647442600001 ()2-s2.0-85105367607 (Scopus ID)
Funder
Swedish Research Council, 2020-01362Region Västerbotten, VLL-582571Region Västerbotten, RV-939171
Available from: 2021-05-25 Created: 2021-05-25 Last updated: 2023-09-05Bibliographically approved
Alam, A., Golovliov, I., Javed, E., Kumar, R., Ådén, J. & Sjöstedt, A. (2020). Dissociation between the critical role of ClpB of Francisella tularensis for the heat shock response and the DnaK interaction and its important role for efficient type VI secretion and bacterial virulence. PLoS Pathogens, 16(4), 1-27, Article ID e1008466.
Open this publication in new window or tab >>Dissociation between the critical role of ClpB of Francisella tularensis for the heat shock response and the DnaK interaction and its important role for efficient type VI secretion and bacterial virulence
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2020 (English)In: PLoS Pathogens, ISSN 1553-7366, E-ISSN 1553-7374, Vol. 16, no 4, p. 1-27, article id e1008466Article in journal (Refereed) Published
Abstract [en]

Author summary Type VI secretion systems (T6SSs) are essential virulence determinants of many Gram-negative pathogens, including Francisella tularensis. This highly virulent bacterium encodes an atypical T6SS lacking ClpV, the ATPase crucial for prototypic T6SS sheath disassembly. It, however, possesses ClpB, a protein critical for heat shock survival via its interaction with DnaK. Since ClpB possesses ATPase activity, it has been hypothesized to provide a compensatory function for the absence of ClpV, a hypothesis supported by the recent findings from us and others. Here, we investigated how F. tularensis ClpB controls T6S. In silico modelling of the ClpB-DnaK complex identified key interactions that were experimentally verified. For example, mutating one of the DnaK-interacting residues rendered the bacterium exquisitely susceptible to heat shock, but had no effect on T6S and virulence. In contrast, removing the N-terminal of ClpB only had a slight effect on the heat shock response, but strongly compromised both T6S and virulence. Intriguingly, the Escherichia coli ClpB could fully complement the function of F. tularensis ClpB. The data demonstrate that the two critical roles of ClpB, mediating heat shock survival and effective T6S, are dissociated and that the N-terminal is crucial for T6S and virulence. Francisella tularensis, a highly infectious, intracellular bacterium possesses an atypical type VI secretion system (T6SS), which is essential for its virulence. The chaperone ClpB, a member of the Hsp100/Clp family, is involved in Francisella T6SS disassembly and type VI secretion (T6S) is impaired in its absence. We asked if the role of ClpB for T6S was related to its prototypical role for the disaggregation activity. The latter is dependent on its interaction with the DnaK/Hsp70 chaperone system. Key residues of the ClpB-DnaK interaction were identified by molecular dynamic simulation and verified by targeted mutagenesis. Using such targeted mutants, it was found that the F. novicida ClpB-DnaK interaction was dispensable for T6S, intracellular replication, and virulence in a mouse model, although essential for handling of heat shock. Moreover, by mutagenesis of key amino acids of the Walker A, Walker B, and Arginine finger motifs of each of the two Nucleotide-Binding Domains, their critical roles for heat shock, T6S, intracellular replication, and virulence were identified. In contrast, the N-terminus was dispensable for heat shock, but required for T6S, intracellular replication, and virulence. Complementation of the Delta clpB mutant with a chimeric F. novicida ClpB expressing the N-terminal of Escherichia coli, led to reconstitution of the wild-type phenotype. Collectively, the data demonstrate that the ClpB-DnaK interaction does not contribute to T6S, whereas the N-terminal and NBD domains displayed critical roles for T6S and virulence.

Place, publisher, year, edition, pages
Public Library of Science, 2020
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-171909 (URN)10.1371/journal.ppat.1008466 (DOI)000531365400029 ()32275693 (PubMedID)2-s2.0-85084105089 (Scopus ID)
Available from: 2020-06-17 Created: 2020-06-17 Last updated: 2023-03-23Bibliographically approved
Alam, A., Golovliov, I., Javed, E. & Sjöstedt, A. (2018). ClpB mutants of Francisella tularensis subspecies holarctica and tularensis are defective for type VI secretion and intracellular replication. Scientific Reports, 8, Article ID 11324.
Open this publication in new window or tab >>ClpB mutants of Francisella tularensis subspecies holarctica and tularensis are defective for type VI secretion and intracellular replication
2018 (English)In: Scientific Reports, E-ISSN 2045-2322, Vol. 8, article id 11324Article in journal (Refereed) Published
Abstract [en]

Francisella tularensis, a highly infectious, intracellular bacterium possesses an atypical type VI secretion system (T6SS), which is essential for the virulence of the bacterium. Recent data suggest that the HSP100 family member, ClpB, is involved in T6SS disassembly in the subspecies Francisella novicida. Here, we investigated the role of ClpB for the function of the T6SS and for phenotypic characteristics of the human pathogenic subspecies holarctica and tularensis. The Delta clpB mutants of the human live vaccine strain, LVS, belonging to subspecies holarctica, and the highly virulent SCHU S4 strain, belonging to subspecies tularensis, both showed extreme susceptibility to heat shock and low pH, severely impaired type VI secretion (T6S), and significant, but impaired intracellular replication compared to the wild-type strains. Moreover, they showed essentially intact phagosomal escape. Infection of mice demonstrated that both Delta clpB mutants were highly attenuated, but the SCHU S4 mutant showed more effective replication than the LVS strain. Collectively, our data demonstrate that ClpB performs multiple functions in the F. tularensis subspecies holarctica and tularensis and its function is important for T6S, intracellular replication, and virulence.

Place, publisher, year, edition, pages
Nature Publishing Group, 2018
National Category
Microbiology in the medical area
Identifiers
urn:nbn:se:umu:diva-150672 (URN)10.1038/s41598-018-29745-4 (DOI)000439965200017 ()30054549 (PubMedID)2-s2.0-85050803246 (Scopus ID)
Funder
Swedish Research Council, 2013-4581; 2013-8621
Available from: 2018-08-16 Created: 2018-08-16 Last updated: 2023-03-24Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-8773-7598

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