Chaperone-assisted pilus assembly and bacterial attachment (original) (raw)
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Therapeutic Approaches Targeting the Assembly and Function of Chaperone-Usher Pili
EcoSal Plus, 2019
The chaperone-usher (CU) pathway is a conserved secretion system dedicated to the assembly of a superfamily of virulence-associated surface structures by a wide range of Gram-negative bacteria. Pilus biogenesis by the CU pathway requires two specialized assembly components: a dedicated periplasmic chaperone and an integral outer membrane assembly and secretion platform termed the usher. The CU pathway assembles a variety of surface fibers, ranging from thin, flexible filaments to rigid, rod-like organelles. Pili typically act as adhesins and function as virulence factors that mediate contact with host cells and colonization of host tissues. Pilus-mediated adhesion is critical for early stages of infection, allowing bacteria to establish a foothold within the host. Pili are also involved in modulation of host cell signaling pathways, bacterial invasion into host cells, and biofilm formation. Pili are critical for initiating and sustaining infection and thus represent attractive targe...
Journal of Bacteriology, 2003
The assembly of type 1 pili on the surface of uropathogenic Escherichia coli proceeds via the chaperone-usher pathway. Chaperone-subunit complexes interact with one another via a process termed donor strand complementation whereby the G1 strand of the chaperone completes the immunoglobulin (Ig) fold of the pilus subunit. Chaperone-subunit complexes are targeted to the usher, which forms a channel across the outer membrane through which pilus subunits are translocated and assembled into pili via a mechanism known as donor strand exchange. This is a mechanism whereby chaperone uncapping from a subunit is coupled with the simultaneous assembly of the subunit into the pilus fiber. Thus, in the pilus fiber, the N-terminal extension of every subunit completes the Ig fold of its neighboring subunit by occupying the same site previously occupied by the chaperone. Here, we investigated details of the donor strand exchange assembly mechanism. We discovered that the information necessary for targeting the FimC-FimH complex to the usher resides mainly in the FimH protein. This interaction is an initiating event in pilus biogenesis. We discovered that the ability of an incoming subunit (in a chaperone-subunit complex) to participate in donor strand exchange with the growing pilus depended on a previously unrecognized function of the chaperone. Furthermore, the donor strand exchange assembly mechanism between subunits was found to be necessary for subunit translocation across the outer membrane usher.
PLOS Pathogens, 2015
Gram-negative pathogens express fibrous adhesive organelles that mediate targeting to sites of infection. The major class of these organelles is assembled via the classical, alternative and archaic chaperone-usher pathways. Although non-classical systems share a wider phylogenetic distribution and are associated with a range of diseases, little is known about their assembly mechanisms. Here we report atomic-resolution insight into the structure and biogenesis of Acinetobacter baumannii Csu and Escherichia coli ECP biofilm-mediating pili. We show that the two non-classical systems are structurally related, but their assembly mechanism is strikingly different from the classical assembly pathway. Non-classical chaperones, unlike their classical counterparts, maintain subunits in a substantially disordered conformational state, akin to a molten globule. This is achieved by a unique binding mechanism involving the register-shifted donor strand complementation and a different subunit carboxylate anchor. The subunit lacks the classical pre-folded initiation site for donor strand exchange, suggesting that recognition of its exposed hydrophobic core starts the assembly process and provides fresh inspiration for the design of inhibitors targeting chaperone-usher systems.
Molecular Microbiology, 2010
Attachment to host cells via adhesive surface structures is a prerequisite for the pathogenesis of many bacteria. Uropathogenic E. coli assemble P and type 1 pili for attachment to the host urothelium. Assembly of these pili requires the conserved chaperone/usher pathway, in which a periplasmic chaperone controls the folding of pilus subunits and an outer membrane usher provides a platform for pilus assembly and secretion. The usher has differential affinity for pilus subunits, with highest affinity for the tip-localized adhesin. Here, we identify residues F21 and R652 of the P pilus usher PapC as functioning in the differential affinity of the usher. R652 is important for high affinity binding to the adhesin whereas F21 is important for limiting affinity for the PapA major rod subunit. PapC mutants in these residues are specifically defective for pilus assembly in the presence of PapA, demonstrating that differential affinity of the usher is required for assembly of complete pili. Analysis of PapG deletion mutants demonstrated that the adhesin is not required to initiate P pilus biogenesis. Thus, the differential affinity of the usher may be critical to ensure assembly of functional pilus fibers.
Structural Basis of Chaperone Function and Pilus Biogenesis
Science, 1999
Many Cram-negative pathogens assemble architecturally and functionally diverse adhesive pili on their surfaces by the chaperone-usher pathway. Immunoglobulin-like periplasmic chaperones escort pilus subunits to the usher, a large protein complex that facilitates the translocation and assembly of subunits across the outer membrane. The crystal structure of the PapD-PapK chaperone-subunit complex, determined at 2.4 angstrom resolution, reveals that the chaperone functions by donating its C, P strand to complete the immunoglobulin-like fold of the subunit via a mechanism termed donor strand complementation. The structure of the PapD-PapK complex also suggests that during pilus biogenesis, every subunit completes the immunoglobulin-like fold of its neighboring subunit via a mechanism termed donor strand exchange.
Chaperone Priming of Pilus Subunits Facilitates a Topological Transition that Drives Fiber Formation
Cell, 2002
bacterial attachment to host tissues, an essential early 2 Department of Biochemistry and Molecular step in UTI pathogenesis (Hultgren et al., 1996). Pilus-Biophysics mediated attachment facilitates bacterial colonization Washington University Medical School and triggers a complex web of events, including signal-660 South Euclid Avenue ing in both the bacterium and host, that then influences St. Louis, Missouri 63105 the course and outcome of the infection (Mulvey et al., 3 Birkbeck College 1998; Martinez et al., 2000; Hung et al., 2001). Department of Crystallography P pili are expressed by many strains of uropathogenic Malet Street E. coli. These pilus fibers are encoded by the pap gene London cluster (papA-K) and bind to the globoseries of glycolip-WC1E 7HX, UK ids present in the human kidney (Hull et al., 1981; Lund 4 The Ludwig Institute for Cancer Research et al., 1987). P pili have been shown to be required University College London for the establishment of pyelonephritis (Roberts et al., 91 Riding House Street 1994). Each P pilus consists of a thick, rigid rod with a London thinner, more flexible tip fibrillum at its distal end. The W1W 7BS, UK rod contains PapA subunits arranged to form a tightly wound, hollow, right-handed helical structure (Gong and Makowski, 1992; Bullitt and Makowski, 1995). The tip Summary fibrillum contains PapE subunits arranged in a more open helical conformation (Kuehn et al., 1992). The PapG Periplasmic chaperones direct the assembly of adheadhesin, which binds the glycolipid receptor, is at the sive, multi-subunit pilus fibers that play critical roles distal end of the tip fibrillum (Kuehn et al., 1992; Dodson in bacterial pathogenesis. Pilus assembly occurs via et al., 2001). The PapF and PapK pilus subunits are a donor strand exchange mechanism in which the N-terthought to link the PapG adhesin to the tip fibrillum and minal extension of one subunit replaces the chaperone the tip fibrillum to the rod, respectively (Jacob-Dubuis-G 1 strand that transiently occupies a groove in the son et al., 1993). neighboring subunit. Here, we show that the chaper-P pili are members of a large family of bacterial surface one primes the subunit for assembly by holding the fibers that are assembled by a conserved secretion and groove in an open, activated conformation. During doassembly system termed the chaperone-usher pathway nor strand exchange, the subunit undergoes a topo-(Thanassi et al., 1998a). This chaperone-usher pathway logical transition that triggers the closure of the groove participates in the assembly of surface organelles in and seals the N-terminal extension in place. It is this many pathogenic bacteria, including uropathogenic and topological transition, made possible only by the primenterotoxigenic E. coli, Haemophilus influenzae, Klebing action of the chaperone that drives subunit assemsiella pneumoniae, Proteus mirabilis, Bordetella pertusbly into the fiber. sis, and Salmonella and Yersinia species, including Yersinia pestis, the causative agent of bubonic plague Introduction (Hung et al.,
The EMBO journal, 1993
Uropathogenic Escherichia coli produce heteropolymeric surface fibers called P pili, which present an adhesin at their tip that specifically recognizes globoside receptors on the host uroepithelium. The initial attachment step is thought to be essential for pathogenesis. P pili are composite fibers consisting of a thin tip fibrillum joined end to end to a rigid helical rod. Here we show that the ordered assembly of these structures requires the activity of two proteins that are minor components of the tip fibrillum, PapF and PapK. PapF is required for the correct presentation of the adhesin at the distal end of the tip fibrillum. PapK regulates the length of the tip fibrillum and joins it to the pilus rod. We propose that these subunits function as adaptors, by providing complementary surfaces to different substructures of the pilus and promoting their proper associations. In addition, the conversion of chaperone-subunit complexes into pili depends on PapF and PapK since a papF- pap...
FEMS Microbiology Reviews, 2010
This review summarizes current knowledge on the structure, function, assembly and biomedical applications of the superfamily of adhesive fimbrial organelles exposed on the surface of Gram-negative pathogens with the classical chaperone/ usher machinery. High-resolution three-dimensional (3D) structure studies of the minifibers assembling with the FGL (having a long F1-G1 loop) and FGS (having a short F1-G1 loop) chaperones show that they exploit the same principle of donorstrand complementation for polymerization of subunits. The 3D structure of adhesive subunits bound to host-cell receptors and the final architecture of adhesive fimbrial organelles reveal two functional families of the organelles, respectively, possessing polyadhesive and monoadhesive binding. The FGL and FGS chaperone-assembled polyadhesins are encoded exclusively by the gene clusters of the g3and k-monophyletic groups, respectively, while gene clusters belonging to the g1-, g2-, g4-, and p-fimbrial clades exclusively encode FGS chaperoneassembled monoadhesins. Novel approaches are suggested for a rational design of antimicrobials inhibiting the organelle assembly or inhibiting their binding to host-cell receptors. Vaccines are currently under development based on the recombinant subunits of adhesins.