| 1. |
- Agarwal, Vaibhav, et al.
(författare)
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A novel interaction between complement inhibitor C4b-binding protein and plasminogen that enhances plasminogen activation.
- 2015
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 290:30, s. 18333-18342
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Tidskriftsartikel (refereegranskat)abstract
- The complement, coagulation and fibrinolytic systems are crucial for the maintenance of tissue homeostasis. To date numerous interactions and cross talks have been identified between these cascades. In line with this, here we propose a novel, hitherto unknown interaction between the complement inhibitor C4b-binding protein (C4BP) and plasminogen of the fibrinolytic pathway. Binding of C4BP to S. pneumoniae is a known virulence mechanism of this pathogen and it was increased in the presence of plasminogen. Interestingly, the acute phase variant of C4BP lacking the β-chain and protein S binds plasminogen much stronger than the main isoform containing the β-chain and protein S. Indeed, the complement control protein (CCP) 8 domain of C4BP, which would otherwise be sterically hindered by the β-chain, primarily mediates this interaction. Moreover, the lysine-binding sites in plasminogen kringle domains facilitate the C4BP-plasminogen interaction. Furthermore, C4BP readily forms complexes with plasminogen in fluid phase and such complexes are present in human serum and plasma. Importantly, while the presence of plasminogen did not affect the factor I cofactor activity of C4BP, the activation of plasminogen by urokinase-type plasminogen activator to active plasmin was significantly augmented in the presence of C4BP. Taken together, our data demonstrate a novel interaction between two proteins of the complement and fibrinolytic system. Most complexes might be formed during the acute phase of inflammation and have an effect on the homeostasis at the site of injury or acute inflammation.
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| 2. |
- Agarwal, Vaibhav, et al.
(författare)
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An Alternative Role of C1q in Bacterial Infections: Facilitating Streptococcus pneumoniae Adherence and Invasion of Host Cells.
- 2013
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Ingår i: Journal of Immunology. - : The American Association of Immunologists. - 1550-6606 .- 0022-1767. ; 191:8, s. 4235-4245
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pneumoniae (pneumococcus) is a major human pathogen, which evolved numerous successful strategies to colonize the host. In this study, we report a novel mechanism of pneumococcal-host interaction, whereby pneumococci use a host complement protein C1q, primarily involved in the host-defense mechanism, for colonization and subsequent dissemination. Using cell-culture infection assays and confocal microscopy, we observed that pneumococcal surface-bound C1q significantly enhanced pneumococcal adherence to and invasion of host epithelial and endothelial cells. Flow cytometry demonstrated a direct, Ab-independent binding of purified C1q to various clinical isolates of pneumococci. This interaction was seemingly capsule serotype independent and mediated by the bacterial surface-exposed proteins, as pretreatment of pneumococci with pronase E but not sodium periodate significantly reduced C1q binding. Moreover, similar binding was observed using C1 complex as the source of C1q. Furthermore, our data show that C1q bound to the pneumococcal surface through the globular heads and with the host cell-surface receptor(s)/glycosaminoglycans via its N-terminal collagen-like stalk, as the presence of C1q N-terminal fragment and low m.w. heparin but not the C-terminal globular heads blocked C1q-mediated pneumococcal adherence to host cells. Taken together, we demonstrate for the first time, to our knowledge, a unique function of complement protein C1q, as a molecular bridge between pneumococci and the host, which promotes bacterial cellular adherence and invasion. Nevertheless, in some conditions, this mechanism could be also beneficial for the host as it may result in uptake and clearance of the bacteria.
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| 3. |
- Agarwal, Vaibhav, et al.
(författare)
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Binding of Streptococcus pneumoniae endopeptidase O (PepO) to complement component C1q modulates the complement attack and promotes host cell adherence.
- 2014
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 289:22, s. 15833-15844
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Tidskriftsartikel (refereegranskat)abstract
- The Gram-positive species Streptococcus pneumoniae is a human pathogen causing severe local and life-threatening invasive diseases associated with high mortality rates and death. We demonstrated recently that pneumococcal endopeptidase O (PepO) is an ubiquitously expressed, multifunctional plasminogen and fibronectin binding protein facilitating host cell invasion and evasion of innate immunity. In this study we found that PepO interacts directly with the complement C1q protein, thereby attenuating the classical complement pathway and facilitating pneumococcal complement escape. PepO binds both free C1q and C1 complex in a dose-dependent manner based on ionic interactions. Our results indicate that recombinant PepO specifically inhibits the classical pathway of complement activation in both hemolytic and complement deposition assays. This inhibition is due to direct interaction of PepO with C1q, leading to a strong activation of the classical complement pathway and results in consumption of complement components. In addition, PepO binds the classical complement pathway inhibitor C4BP, thereby regulating downstream complement activation. Importantly, pneumococcal surface-exposed PepO-C1q interaction mediates bacterial adherence to host epithelial cells. Taken together, PepO facilitates C1q-mediated bacterial adherence, while its localized release consumes complement as a result of its activation following binding of C1q, thus representing an additional mechanism of human complement escape by this versatile pathogen.
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| 4. |
- Agarwal, Vaibhav, et al.
(författare)
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Enolase of Streptococcus pneumoniae Binds Human Complement Inhibitor C4b-Binding Protein and Contributes to Complement Evasion.
- 2012
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Ingår i: Journal of immunology. - : The American Association of Immunologists. - 1550-6606 .- 0022-1767. ; 189:7, s. 3575-3584
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pneumoniae (pneumococcus) is a pathogen that causes severe local and life-threatening invasive diseases, which are associated with high mortality rates. Pneumococci have evolved several strategies to evade the host immune system, including complement to disseminate and to survive in various host niches. Thus, pneumococci bind complement inhibitors such as C4b-binding protein (C4BP) and factor H via pneumococcal surface protein C, thereby inhibiting the classical and alternative complement pathways. In this study, we identified the pneumococcal glycolytic enzyme enolase, a nonclassical cell surface and plasminogen-binding protein, as an additional pneumococcal C4BP-binding protein. Furthermore, we demonstrated that human, but not mouse, C4BP bound pneumococci. Recombinant enolase bound in a dose-dependent manner C4BP purified from plasma, and the interaction was reduced by increasing ionic strength. Enolase recruited C4BP and plasminogen, but not factor H, from human serum. Moreover, C4BP and plasminogen bound to different domains of enolase as they did not compete for the interaction with enolase. In direct binding assays with recombinant C4BP mutants lacking individual domains, two binding sites for enolase were identified on the complement control protein (CCP) domain 1/CCP2 and CCP8 of the C4BP α-chains. C4BP bound to the enolase retained its cofactor activity as determined by C4b degradation. Furthermore, in the presence of exogenously added enolase, an increased C4BP binding to and subsequently decreased C3b deposition on pneumococci was observed. Taken together, pneumococci specifically interact with human C4BP via enolase, which represents an additional mechanism of human complement control by this versatile pathogen.
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| 5. |
- Agarwal, Vaibhav, et al.
(författare)
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Roles of Complement C1q in Pneumococcus-Host Interactions.
- 2015
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Ingår i: Critical Reviews in Immunology. - 1040-8401. ; 35:3, s. 173-184
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Tidskriftsartikel (refereegranskat)abstract
- The fight between a human host and a bacterial pathogen is highly complicated; each party tries to outshine the other in the race for survival. In humans, the innate immune system-in particular the complement system-functions as the first line of defence against invading pathogens. During the course of evolution, however, pathogens, in order to survive and perpetuate within a host, developed multiple strategies to counteract the host complement system and to colonize. One such pathogen is Streptococcus pneumoniae (pneumococcus), a gram-positive bacterial pathogen often commensal in the human respiratory tract. Depending on the host's susceptibility, pneumococci can transform into an infectious agent, disseminating within the human host and causing mild to life-threatening diseases. This transition from commensal to infectious agent is a highly complex process, and understanding of this mechanism is essential in controlling the pathogenicity of pneumococci. Using its intricate arsenal of weapons, such as surface-presenting adhesins as well as recruitment of host factor, pneumococci successfully colonize the host, a prerequisite for establishing infection. This review describes C1q, the first subunit of the classical complement pathway, and its role in pneumococcus-host interactions, whereby pneumococci exploit C1q as a molecular bridge facilitating host cellular adherence and invasion, a function not akin to the role of C1q in the defence mechanism.
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| 6. |
- Agarwal, Vaibhav, et al.
(författare)
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Streptococcus pneumoniae endopeptidase O (PepO): a multifunctional plasminogen and fibronectin binding protein, facilitating evasion of innate immunity and invasion of host cells.
- 2013
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 288:10, s. 6849-6863
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pneumoniae infections remain a major cause of morbidity and mortality worldwide. Therefore a detailed understanding and characterization of the mechanism of host cell colonization and dissemination is critical in order to gain control over this versatile pathogen. Here we identified a novel 72 kDa pneumococcal protein endopeptidase O (PepO), as a plasminogen and fibronectin binding protein. Using a collection of clinical isolates, representing different serotypes, we found PepO to be ubiquitously present both at the gene and at the protein level. In addition, PepO protein was secreted in a growth-phase dependent manner to the culture supernatants of the pneumococcal isolates. Recombinant PepO bound human plasminogen and fibronectin in a dose-dependent manner and plasminogen did not compete with fibronectin for binding PepO. PepO bound plasminogen via lysine residues and the interaction was influenced by ionic strength. Moreover, upon activation of PepO bound plasminogen by urokinase-type plasminogen activator, generated plasmin cleaved complement protein C3b thus assisting in complement control. Furthermore, direct binding assays demonstrated the interaction of PepO with epithelial and endothelial cells that in turn blocked pneumococcal adherence. Moreover, a pepO-mutant strain showed impaired adherence to and invasion of host cells compared to their isogenic wild-type strains. Taken together, the results demonstrated that PepO is ubiquitously expressed plasminogen and fibronectin binding protein, which plays role in pneumococcal invasion of host cells and aids in immune evasion.
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| 7. |
- Asmat, Tauseef M, et al.
(författare)
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Endocytosis of Streptococcus pneumoniae via the polymeric immunoglobulin receptor of epithelial cells relies on clathrin and caveolin dependent mechanisms.
- 2014
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Ingår i: International Journal of Medical Microbiology. - : Elsevier BV. - 1618-0607 .- 1438-4221. ; 304:8, s. 1233-1246
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Tidskriftsartikel (refereegranskat)abstract
- Colonization of Streptococcus pneumoniae (pneumococci) is a prerequisite for bacterial dissemination and their capability to enter the bloodstream. Pneumococci have evolved various successful strategies to colonize the mucosal epithelial barrier of humans. A pivotal mechanism of host cell invasion implicated with invasive diseases is promoted by the interaction of pneumococcal PspC with the polymeric Ig-receptor (pIgR). However, the mechanism(s) of pneumococcal endocytosis and the intracellular route of pneumococci upon uptake by the PspC-pIgR-interaction are not known. Here, we demonstrate by using a combination of pharmacological inhibitors and genetics interference approaches the involvement of active dynamin-dependent caveolae and clathrin-coated vesicles for pneumococcal uptake via the PspC-pIgR mechanism. Depleting cholesterol from host cell membranes and disruption of lipid microdomains impaired pneumococcal internalization. Moreover, chemical inhibition of clathrin or functional inactivation of dynamin, caveolae or clathrin by RNA interference significantly affected pneumococcal internalization suggesting that clathrin-mediated endocytosis (CME) and caveolae are involved in the bacterial uptake process. Confocal fluorescence microscopy of pIgR-expressing epithelial cells infected with pneumococci or heterologous Lactococcus lactis expressing PspC demonstrated bacterial co-localization with fluorescent-tagged clathrin and early as well as recycling or late endosomal markers such as Lamp1, Rab5, Rab4, and Rab7, respectively. In conclusion these data suggest that PspC-promoted uptake is mediated by both CME and caveolae. After endocytosis pneumococci are routed via the endocytic pathway into early endosomes and are then sorted into recycling or late endosomes, which can result in pneumococcal killing in phagolysosomes or transcytosis via recycling endosomes.
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| 8. |
- Bergmann, Simone, et al.
(författare)
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Exploitation of Host Signal Transduction Pathways Induced by Streptococcus pneumoniae
- 2015
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Ingår i: Streptococcus Pneumoniae : Molecular Mechanisms of Host-Pathogen Interactions - Molecular Mechanisms of Host-Pathogen Interactions. - 9780124105300 - 9780124114531 ; , s. 347-362
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Bokkapitel (refereegranskat)abstract
- The induction of host signal transduction cascades by bacterial pathogens contributes directly to their virulence. In addition to the pore-forming cytolysin pneumolysin, several surface-exposed proteins of Streptococcus pneumoniae are also potent modulators of complex host signaling pathways. These pneumococcal surface proteins either directly mediate adhesion of pneumococci to specific cell surface receptors or recruit extracellular matrix or serum components as molecular bridges for binding to cellular receptors. In turn, adhesion triggers and subverts host signal transduction cascades to promote pneumococcal translocation across tissue barriers and dissemination within host tissues. This chapter summarizes the current knowledge of how pneumolysin and major adhesins manipulate host signaling pathways. The chapter will provide a structured overview of the signaling profiles induced by pneumococci, focusing on the receptors required and comparing the key signaling molecules and intracellular responses involved.
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| 9. |
- Blom, Anna, et al.
(författare)
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Streptococcus pneumoniae phosphoglycerate kinase is a novel complement inhibitor affecting the membrane attack complex formation.
- 2014
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 289:47
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Tidskriftsartikel (refereegranskat)abstract
- The Gram-positive bacterium Streptococcus pneumoniae is a major human pathogen that causes infections ranging from acute otitis media to life-threatening invasive disease. Pneumococci have evolved several strategies to circumvent the host immune response, in particular the complement attack. The pneumococcal glycolytic enzyme phosphoglycerate kinase (PGK) is both secreted and bound to the bacterial surface and simultaneously binds plasminogen and its activator tPA. In the present study, we demonstrate that PGK has an additional role in modulating the complement attack. PGK interacted with the membrane attack complex (MAC) components C5, C7 and C9, thereby blocking the assembly and membrane insertion of MAC resulting in significant inhibition of the hemolytic activity of human serum. Recombinant PGK interacted in a dose-dependent manner with these terminal pathway proteins, and the interactions were ionic in nature. In addition, PGK inhibited C9 polymerization both in the fluid phase and on the surface of sheep erythrocytes. Interestingly, PGK bound several MAC proteins simultaneously. While C5 and C7 had partially overlapping binding sites on PGK, C9 did not compete with either one for PGK binding. Moreover, PGK significantly inhibited MAC deposition via both the classical and alternative pathway at the pneumococcal surface. Additionally, upon activation plasmin(ogen) bound to PGK cleaved the central complement protein C3b thereby further modifying the complement attack. In conclusion, our data demonstrate for the first time, to our knowledge, a novel pneumococcal inhibitor of the terminal complement cascade aiding complement evasion by this important pathogen.
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| 10. |
- Ermert, David, et al.
(författare)
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Binding of complement inhibitor C4b-binding protein to a highly virulent S. pyogenes M1 strain is mediated by protein H and enhances adhesion to and invasion of endothelial cells.
- 2013
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Ingår i: Journal of Biological Chemistry. - 1083-351X. ; 288:45, s. 32172-32183
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Tidskriftsartikel (refereegranskat)abstract
- Streptococcus pyogenes AP1, a strain of the highly virulent M1 serotype, uses exclusively protein H to bind the complement inhibitor C4b-binding protein (C4BP). We found a strong correlation between the ability of AP1 and its isogenic mutants lacking protein H to inhibit opsonisation with complement C3b and binding of C4BP. C4BP bound to immobilized protein H or AP1 bacteria retained its cofactor activity for degradation of 125I-C4b. Further, C4b deposited from serum onto AP1 bacterial surfaces was processed into C4c/C4d fragments, which did not occur on strains unable to bind C4BP. Recombinant C4BP mutants, which (i) lack certain CCP domains, or (ii) have mutations in single aa as well as (iii) mutants with additional aa between different CCP domains were used to determine that the binding is mainly mediated by a patch of positively charged amino acid residues at the interface of domains CCP1 and CCP2. Using recombinant protein H fragments, we narrowed down the binding site to the N-terminal domain A. With a peptide microarray, we identified one single 18 amino acid long peptide comprising residues 92-109, which specifically bound C4BP. Biacore was used to determine KD = 6x10-7 M between protein H and a single subunit of C4BP. C4BP binding also correlated with elevated levels of adhesion and invasion to endothelial cells. Taken together, we identified the molecular basis of C4BP-protein H interaction and found that it is not only important for decreased opsonisation but also for invasion of endothelial cells by Streptococcus pyogenes.
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| 11. |
- Liu, Guanghui, et al.
(författare)
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Moraxella catarrhalis Evades Host Innate Immunity via Targeting Cartilage Oligomeric Matrix Protein.
- 2016
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Ingår i: Journal of Immunology. - : The American Association of Immunologists. - 1550-6606 .- 0022-1767. ; 196:3, s. 1249-1258
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Tidskriftsartikel (refereegranskat)abstract
- Moraxella catarrhalis is a respiratory tract pathogen commonly causing otitis media in children and acute exacerbations in patients suffering from chronic obstructive pulmonary disease. Cartilage oligomeric matrix protein (COMP) functions as a structural component in cartilage, as well as a regulator of complement activity. Importantly, COMP is detected in resident macrophages and monocytes, alveolar fluid, and the endothelium of blood vessels in lung tissue. We show that the majority of clinical isolates of M. catarrhalis (n = 49), but not other tested bacterial pathogens, bind large amounts of COMP. COMP interacts directly with the ubiquitous surface protein A2 of M. catarrhalis. Binding of COMP correlates with survival of M. catarrhalis in human serum by inhibiting bactericidal activity of the complement membrane attack complex. Moreover, COMP inhibits phagocytic killing of M. catarrhalis by human neutrophils. We further observed that COMP reduces bacterial adhesion and uptake by human lung epithelial cells, thus protecting M. catarrhalis from intracellular killing by epithelial cells. Taken together, our findings uncover a novel mechanism that M. catarrhalis uses to evade host innate immunity.
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| 12. |
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| 13. |
- Manne, Kartik, et al.
(författare)
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Novel structure of the N-terminal helical domain of BibA, a group B streptococcus immunogenic bacterial adhesin
- 2020
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Ingår i: Acta crystallographica. Section D, Structural biology. - 2059-7983. ; 76, s. 759-770
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Tidskriftsartikel (refereegranskat)abstract
- BibA, a group B streptococcus (GBS) surface protein, has been shown to protect the pathogen from phagocytic killing by sequestering a complement inhibitor: C4b-binding protein (C4BP). Here, the X-ray crystallographic structure of a GBS BibA fragment (BibA126-398) and a low-resolution small-angle X-ray scattering (SAXS) structure of the full-length N-terminal domain (BibA34-400) are described. The BibA126-398 fragment crystal structure displayed a novel and predominantly helical structure. The tertiary arrangement of helices forms four antiparallel three-helix-bundle-motif repeats, with one long helix from a bundle extending into the next. Multiple mutations on recombinant BibA34-400 delayed the degradation of the protein, and circular dichroism spectroscopy of BibA34-400 suggested a similar secondary-structure composition to that observed in the crystallized BibA126-398 fragment. A model was generated for the 92 N-terminal residues (BibA34-125) using structural similarity prediction programs, and a BibA34-400 model was generated by combining the coordinates of BibA34-126 and BibA126-398. The X-ray structure of BibA126-398 and the model of BibA34-400 fitted well into the calculated SAXS envelope. One possible binding site for the BibA N-terminal domain was localized to the N-terminal CCP (complement-control protein) domains of the C4BP α-chain, as indicated by the decreased binding of BibA to a ΔCCP1 C4BP α-chain mutant. In summary, it is suggested that the GBS surface protein BibA, which consists of three antiparallel α-helical-bundle motifs, is unique and belongs to a new class of Gram-positive surface adhesins.
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| 14. |
- Richter, Corinna, et al.
(författare)
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Moonlighting of Helicobacter pylori catalase protects against complement-mediated killing by utilising the host molecule vitronectin
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Helicobacter pylori is an important human pathogen and a common cause of peptic ulcers and gastric cancer. Despite H. pylori provoking strong innate and adaptive immune responses, the bacterium is able to successfully establish long-term infections. Vitronectin (Vn), a component of both the extracellular matrix and plasma, is involved in many physiological processes, including regulation of the complement system. The aim of this study was to define a receptor in H. pylori that binds Vn and determine the significance of the interaction for virulence. Surprisingly, by using proteomics, we found that the hydrogen peroxide-neutralizing enzyme catalase KatA is a major Vn-binding protein. Deletion of the katA gene in three different strains resulted in impaired binding of Vn. Recombinant KatA was generated and shown to bind with high affinity to a region between heparin-binding domain 2 and 3 of Vn that differs from previously characterised bacterial binding sites on the molecule. In terms of function, KatA protected H. pylori from complement-mediated killing in a Vn-dependent manner. Taken together, the virulence factor KatA is a Vn-binding protein that moonlights on the surface of H. pylori to promote bacterial evasion of host innate immunity.
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