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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 52 (2004), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Type IV pili (Tfps) are filamentous surface appendages expressed by Gram-negative microorganisms and play numerous roles in bacterial cell biology. Tfp biogenesis machineries are highly conserved and resemble protein secretion and DNA uptake systems. Although components of Tfp biogenesis systems have been identified, it is not known how they interact to form these machineries. Using the bundle-forming pilus (BFP) of enteropathogenic Escherichia coli as a model Tfp system, we provide evidence of a cytoplasmic membrane subassembly of the Tfp assembly machine composed of putative cytoplasmic nucleotide-binding and cytoplasmic membrane proteins. A combination of genetic, biochemical and biophysical approaches revealed interactions among putative cytoplasmic nucleotide-binding proteins BfpD and BfpF and cytoplasmic membrane proteins BfpC and BfpE of the BFP biogenesis machine. The polytopic membrane protein BfpE appears to be a central component of this subassembly as it interacts with BfpC, BfpD and BfpF. We report that BFP biogenesis probably requires interactions among BfpC, BfpD and BfpE, whereas BFP retraction requires interaction of the PilT-like putative ATPase BfpF with a conserved domain of BfpE. BfpE is the first protein that is not a member of the PilT family to be implicated in Tfp retraction. Furthermore, we found that the putative ATPases BfpD and BfpF play antagonistic roles in BFP biogenesis and retraction, respectively, by interacting with distinct domains of the BFP biogenesis machine.
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  • 2
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Enteropathogenic Escherichia coli (EPEC), an important cause of infantile diarrhoea in the developing world, disrupts host cell microvilli, causes actin rearrangements and attaches intimately to the host cell surface. This characteristic phenotype, referred to as the attaching and effacing (A/E) effect, is encoded on a 36 kb pathogenicity island called the locus of enterocyte effacement (LEE). The LEE includes genes involved in type III secretion and translocation, the eae gene encoding an outer membrane adhesin known as intimin, the tir gene for the translocated intimin receptor, a regulator and various genes of unknown function. Among this last group is sepL. To determine the role of SepL in EPEC pathogenesis, we constructed and tested a non-polar sepL mutant. We found that this sepL mutant is deficient for A/E and that it secretes markedly reduced quantities of those proteins involved in translocation (EspA, EspB and EspD), but normal levels of those proteins presumed to be effectors (Tir, EspF and EspG). Despite normal levels of secretion, the mutant strain was unable to translocate EspF and Tir into host cells and formed no EspA filaments. Fractionation studies revealed that SepL is a soluble cytoplasmic protein. Yeast two-hybrid and affinity purification studies indicated that SepL interacts with the LEE-encoded protein SepD. In contrast to SepL, we found that SepD is required for type III secretion of both translocation and effector proteins. Together, these results demonstrate that SepL has a unique role in type III secretion as a functional component of the translocation system that interacts with an essential element of the secretion machinery.
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