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ATPase-independent type-III protein secretion in Salmonella enterica.

Erhardt M, Mertens ME, Fabiani FD, Hughes KT - PLoS Genet. (2014)

Bottom Line: Type-III protein secretion systems are utilized by gram-negative pathogens to secrete building blocks of the bacterial flagellum, virulence effectors from the cytoplasm into host cells, and structural subunits of the needle complex.We additionally show that increased proton motive force bypassed the requirement of the Salmonella pathogenicity island 1 virulence-associated type-III ATPase for secretion.Our data support a role for type-III ATPases in enhancing secretion efficiency under limited secretion substrate concentrations and reveal the dispensability of ATPase activity in the type-III protein export process.

View Article: PubMed Central - PubMed

Affiliation: Junior Research Group Infection Biology of Salmonella, Helmholtz Centre for Infection Research, Braunschweig, Germany.

ABSTRACT
Type-III protein secretion systems are utilized by gram-negative pathogens to secrete building blocks of the bacterial flagellum, virulence effectors from the cytoplasm into host cells, and structural subunits of the needle complex. The flagellar type-III secretion apparatus utilizes both the energy of the proton motive force and ATP hydrolysis to energize substrate unfolding and translocation. We report formation of functional flagella in the absence of type-III ATPase activity by mutations that increased the proton motive force and flagellar substrate levels. We additionally show that increased proton motive force bypassed the requirement of the Salmonella pathogenicity island 1 virulence-associated type-III ATPase for secretion. Our data support a role for type-III ATPases in enhancing secretion efficiency under limited secretion substrate concentrations and reveal the dispensability of ATPase activity in the type-III protein export process.

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Schematic overview of the flagellar transcriptional hierarchy and biogenesis.The flagellar transcriptional hierarchy of Salmonella enterica is composed of three classes of promoters. The Class I promoter transcribes a single operon encoding for the master regulator of the flagellar transcriptional hierarchy, the FlhD4C2 complex, which is negatively regulated by ClpXP protease. FlhD4C2, together with σ70, directs RNA polymerase to transcribe from Class II promoters. Genes transcribed from Class II promoters encode structural components of the hook-basal-body complex (shaded in blue), the flagellar type-III secretion apparatus (composed of the membrane proteins FlhA, FlhB, FliO, FliP, FliQ and FliR; and the soluble proteins FliH, FliI and FliJ), as well as regulatory proteins, in particular the flagellar-specific σ-factor, σ28 (encoded by fliA), and its cognate anti-σ factor, FlgM. The hook-basal-body is completed as soon as the hook reaches an approximate length of 55 nm, upon which the type-III secretion apparatus switches secretion specificity to its late-substrate secretion mode (indicated by the orange star). Subsequently, the late substrate FlgM is exported out of the cell, thereby freeing σ28 to turn on transcription from Class III promoters. Class III gene products include the filament subunits, motor-force generators and the chemotactic system (shaded in red).
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pgen-1004800-g001: Schematic overview of the flagellar transcriptional hierarchy and biogenesis.The flagellar transcriptional hierarchy of Salmonella enterica is composed of three classes of promoters. The Class I promoter transcribes a single operon encoding for the master regulator of the flagellar transcriptional hierarchy, the FlhD4C2 complex, which is negatively regulated by ClpXP protease. FlhD4C2, together with σ70, directs RNA polymerase to transcribe from Class II promoters. Genes transcribed from Class II promoters encode structural components of the hook-basal-body complex (shaded in blue), the flagellar type-III secretion apparatus (composed of the membrane proteins FlhA, FlhB, FliO, FliP, FliQ and FliR; and the soluble proteins FliH, FliI and FliJ), as well as regulatory proteins, in particular the flagellar-specific σ-factor, σ28 (encoded by fliA), and its cognate anti-σ factor, FlgM. The hook-basal-body is completed as soon as the hook reaches an approximate length of 55 nm, upon which the type-III secretion apparatus switches secretion specificity to its late-substrate secretion mode (indicated by the orange star). Subsequently, the late substrate FlgM is exported out of the cell, thereby freeing σ28 to turn on transcription from Class III promoters. Class III gene products include the filament subunits, motor-force generators and the chemotactic system (shaded in red).

Mentions: Many bacteria move by rotating a rigid, helical organelle, the flagellum [1]. The flagellum represents one of the smallest motor complexes known and enables bacteria to move through liquids (swimming) [2] and highly viscous environments or surfaces (swarming) [3]. In addition to the chemotactic behavior, flagellar motility contributes to bacterial pathogenesis by promoting bacteria-host interactions, adherence, biofilm formation and invasion of eukaryotic cells [4]. A schematic overview of flagellar biogenesis in Salmonella enterica is shown in Figure 1. Export of the building blocks of the flagellum is mediated by a flagellar-specific type-III secretion system (fT3SS), whose core cytoplasmic and inner-membrane export apparatus components (FliHIJ FliPQR FlhAB) are evolutionarily and functionally related to the virulence-associated type-III secretion systems (vT3SS) of pathogenic Gram-negative bacteria [5].


ATPase-independent type-III protein secretion in Salmonella enterica.

Erhardt M, Mertens ME, Fabiani FD, Hughes KT - PLoS Genet. (2014)

Schematic overview of the flagellar transcriptional hierarchy and biogenesis.The flagellar transcriptional hierarchy of Salmonella enterica is composed of three classes of promoters. The Class I promoter transcribes a single operon encoding for the master regulator of the flagellar transcriptional hierarchy, the FlhD4C2 complex, which is negatively regulated by ClpXP protease. FlhD4C2, together with σ70, directs RNA polymerase to transcribe from Class II promoters. Genes transcribed from Class II promoters encode structural components of the hook-basal-body complex (shaded in blue), the flagellar type-III secretion apparatus (composed of the membrane proteins FlhA, FlhB, FliO, FliP, FliQ and FliR; and the soluble proteins FliH, FliI and FliJ), as well as regulatory proteins, in particular the flagellar-specific σ-factor, σ28 (encoded by fliA), and its cognate anti-σ factor, FlgM. The hook-basal-body is completed as soon as the hook reaches an approximate length of 55 nm, upon which the type-III secretion apparatus switches secretion specificity to its late-substrate secretion mode (indicated by the orange star). Subsequently, the late substrate FlgM is exported out of the cell, thereby freeing σ28 to turn on transcription from Class III promoters. Class III gene products include the filament subunits, motor-force generators and the chemotactic system (shaded in red).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4230889&req=5

pgen-1004800-g001: Schematic overview of the flagellar transcriptional hierarchy and biogenesis.The flagellar transcriptional hierarchy of Salmonella enterica is composed of three classes of promoters. The Class I promoter transcribes a single operon encoding for the master regulator of the flagellar transcriptional hierarchy, the FlhD4C2 complex, which is negatively regulated by ClpXP protease. FlhD4C2, together with σ70, directs RNA polymerase to transcribe from Class II promoters. Genes transcribed from Class II promoters encode structural components of the hook-basal-body complex (shaded in blue), the flagellar type-III secretion apparatus (composed of the membrane proteins FlhA, FlhB, FliO, FliP, FliQ and FliR; and the soluble proteins FliH, FliI and FliJ), as well as regulatory proteins, in particular the flagellar-specific σ-factor, σ28 (encoded by fliA), and its cognate anti-σ factor, FlgM. The hook-basal-body is completed as soon as the hook reaches an approximate length of 55 nm, upon which the type-III secretion apparatus switches secretion specificity to its late-substrate secretion mode (indicated by the orange star). Subsequently, the late substrate FlgM is exported out of the cell, thereby freeing σ28 to turn on transcription from Class III promoters. Class III gene products include the filament subunits, motor-force generators and the chemotactic system (shaded in red).
Mentions: Many bacteria move by rotating a rigid, helical organelle, the flagellum [1]. The flagellum represents one of the smallest motor complexes known and enables bacteria to move through liquids (swimming) [2] and highly viscous environments or surfaces (swarming) [3]. In addition to the chemotactic behavior, flagellar motility contributes to bacterial pathogenesis by promoting bacteria-host interactions, adherence, biofilm formation and invasion of eukaryotic cells [4]. A schematic overview of flagellar biogenesis in Salmonella enterica is shown in Figure 1. Export of the building blocks of the flagellum is mediated by a flagellar-specific type-III secretion system (fT3SS), whose core cytoplasmic and inner-membrane export apparatus components (FliHIJ FliPQR FlhAB) are evolutionarily and functionally related to the virulence-associated type-III secretion systems (vT3SS) of pathogenic Gram-negative bacteria [5].

Bottom Line: Type-III protein secretion systems are utilized by gram-negative pathogens to secrete building blocks of the bacterial flagellum, virulence effectors from the cytoplasm into host cells, and structural subunits of the needle complex.We additionally show that increased proton motive force bypassed the requirement of the Salmonella pathogenicity island 1 virulence-associated type-III ATPase for secretion.Our data support a role for type-III ATPases in enhancing secretion efficiency under limited secretion substrate concentrations and reveal the dispensability of ATPase activity in the type-III protein export process.

View Article: PubMed Central - PubMed

Affiliation: Junior Research Group Infection Biology of Salmonella, Helmholtz Centre for Infection Research, Braunschweig, Germany.

ABSTRACT
Type-III protein secretion systems are utilized by gram-negative pathogens to secrete building blocks of the bacterial flagellum, virulence effectors from the cytoplasm into host cells, and structural subunits of the needle complex. The flagellar type-III secretion apparatus utilizes both the energy of the proton motive force and ATP hydrolysis to energize substrate unfolding and translocation. We report formation of functional flagella in the absence of type-III ATPase activity by mutations that increased the proton motive force and flagellar substrate levels. We additionally show that increased proton motive force bypassed the requirement of the Salmonella pathogenicity island 1 virulence-associated type-III ATPase for secretion. Our data support a role for type-III ATPases in enhancing secretion efficiency under limited secretion substrate concentrations and reveal the dispensability of ATPase activity in the type-III protein export process.

Show MeSH
Related in: MedlinePlus