Structure of CfaA Suggests a New Family of Chaperones Essential for Assembly of Class 5 Fimbriae

Bao, Rui; Fordyce, April; Yuxing, Chen; McVeigh, Annette L.; Savarino, Stephen J.; Xia, Di

doi:10.1371/journal.ppat.1004316

Cited by 8 publications

(25 citation statements)

References 47 publications

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“…coli and Yersinia pestis . The crystal structure of chaperone CfaA has been recently determined [ 20 ], providing an opportunity to compare chaperones between these subfamilies ( Fig 7B ). Expectedly, superposition of N-terminal domains in EcpB and CfaA shows significant structural similarity (Z-score of 12.7, S2 Table ).…”

Section: Resultsmentioning

confidence: 99%

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Structural Insight into Archaic and Alternative Chaperone-Usher Pathways Reveals a Novel Mechanism of Pilus Biogenesis

et al. 2015

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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.

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Section: Resultsmentioning

confidence: 99%

“…Residues that form ionic or hydrogen bonds with the super-conserved arginine, anchoring C-terminal carboxylate of subunits, are shown by shading in blue ( S11 Fig ). CLUSTALW alignment of sequences was modified based on superposition of structures of CsuC (this study), EcpB (this study) and CfaA [ 20 ].…”

Section: Supporting Informationmentioning

confidence: 99%

Structural Insight into Archaic and Alternative Chaperone-Usher Pathways Reveals a Novel Mechanism of Pilus Biogenesis

et al. 2015

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“…Molecular replacement was attempted with AMoRe (Navaza, 2001), MOLREP (Vagin & Teplyakov, 2010), Phaser (McCoy, 2007 and within MR_Rosetta (Terwilliger et al, 2012) using all known structures of chaperone-usher pathway chaperones as search models: CupB2 (PDB entry 3q48; Cai et al, 2011), SafB (PDB entry 2co7; Remaut et al, 2006), DraB (PDB entry 4djm; Z. Dauter, R. Piatek, M. Dauter & A. Brzuszkiewicz, unpublished work), FimC (PDB entry 1klf; Hung et al, 2002), Caf1M (PDB entry 4ay0; Yu et al, 2012), PapD (PDB entry 2xg5; Chorell et al, 2010), CfaA (PDB entry 4ncd; Bao et al, 2014), SfaE (PDB entry 1l4i; Knight et al, 2002) and FaeE (PDB entry 3gfu; Van Molle et al, 2009). Unfortunately, no solutions were found; however, the sequence identity between EcpB and these homologues is less than 20%.…”

Section: Figurementioning

confidence: 99%

Purification, crystallization and preliminary X-ray diffraction analysis of theEscherichia colicommon pilus chaperone EcpB

2015

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Pili are key cell-surface components that allow the attachment of bacteria to both biological and abiotic solid surfaces, whilst also mediating interactions between themselves. InEscherichia coli, the common pilus (Ecp) belongs to an alternative chaperone–usher (CU) pathway that plays a major role in both early biofilm formation and host-cell adhesion. The chaperone EcpB is involved in the biogenesis of the filament, which is composed of EcpA and EcpD. Initial attempts at crystallizing EcpB using natively purified protein from the bacterial periplasm were not successful; however, after the isolation of EcpB under denaturing conditions and subsequent refolding, crystals were obtained at pH 8.0 using the sitting-drop method of vapour diffusion. Diffraction data have been processed to 2.4 Å resolution. These crystals belonged to the trigonal space groupP3121 orP3221, with unit-cell parametersa=b= 62.65,c= 121.14 Å and one monomer in the asymmetric unit. Molecular replacement was unsuccessful, but selenomethionine-substituted protein and heavy-atom derivatives are being prepared for phasing. The three-dimensional structure of EcpB will provide invaluable information on the subtle mechanistic differences in biogenesis between the alternative and classical CU pathways. Furthermore, this is the first time that this refolding strategy has been used to purify CU chaperones, and it could be implemented in similar systems where it has not been possible to obtain highly ordered crystals.

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“…Certain sequence motifs are typical of CUP fimbriae, including alternating hydrophobic residues at the C‐terminus of their pilins (Dodson et al ., ; Nishiyama et al ., 2005; 2008). The pilins of Class 5 fimbriae, of which ETEC colonization factor antigen I (CFA/I) fimbria is the archetypal member, do not share this or other signature motifs with CUP fimbriae and are assembled by what has been termed the alternate chaperone pathway (ACP), using chaperones distinct from those of the CUP (Soto and Hultgren, ; Bao et al ., ).…”

Section: Introductionmentioning

confidence: 97%

Structure and function of enterotoxigenic Escherichia coli fimbriae from differing assembly pathways

Mortezaei

Epler

Shao

et al. 2014

Molecular Microbiology

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Pathogenic enterotoxigenic Escherichia coli (ETEC) are the major bacterial cause of diarrhea in young children in developing countries and in travelers, causing significant mortality in children. Adhesive fimbriae are a prime virulence factor for ETEC, initiating colonization of the small intestinal epithelium. Similar to other Gram-negative bacteria, ETEC express one or more diverse fimbriae, some assembled by the chaperone-usher pathway and others by the alternate chaperone pathway. Here we elucidate structural and biophysical aspects and adaptations of each fimbrial type to its respective host niche. CS20 fimbriae are compared to CFA/I fimbriae, which are two ETEC fimbriae assembled via different pathways, and to P-fimbriae from uropathogenic E. coli. Many fimbriae unwind from their native helical filament to an extended linear conformation under force, thereby sustaining adhesion by reducing load at the point of contact between the bacterium and the target cell. CFA/I fimbriae require the least force to unwind, followed by CS20 fimbriae and then P-fimbriae, which require the highest unwinding force. We conclude from our electron microscopy reconstructions, modeling, and force spectroscopy data that the target niche plays a central role in the biophysical properties of fimbriae that are critical for bacterial pathophysiology.

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Structure of CfaA Suggests a New Family of Chaperones Essential for Assembly of Class 5 Fimbriae

Cited by 8 publications

References 47 publications

Structural Insight into Archaic and Alternative Chaperone-Usher Pathways Reveals a Novel Mechanism of Pilus Biogenesis

Structural Insight into Archaic and Alternative Chaperone-Usher Pathways Reveals a Novel Mechanism of Pilus Biogenesis

Purification, crystallization and preliminary X-ray diffraction analysis of theEscherichia colicommon pilus chaperone EcpB

Structure and function of enterotoxigenic Escherichia coli fimbriae from differing assembly pathways

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