title: Structural Insight into Archaic and Alternative Chaperone-Usher Pathways Reveals a Novel Mechanism of Pilus Biogenesis.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Turku, Turku, JBL, Arcanum, Turku, Finland.
authors.forename: Natalia
authors.initials: N
authors.lastname: Pakharukova
authors.affiliation: Centre for Structural Biology, Department of Life Sciences, Imperial College London, South Kensington, London, United Kingdom.
authors.forename: James A
authors.initials: JA
authors.lastname: Garnett
authors.affiliation: Department of Chemistry, University of Turku, Turku, JBL, Arcanum, Turku, Finland.
authors.forename: Minna
authors.initials: M
authors.lastname: Tuittila
authors.affiliation: Department of Chemistry, University of Turku, Turku, JBL, Arcanum, Turku, Finland.
authors.forename: Sari
authors.initials: S
authors.lastname: Paavilainen
authors.affiliation: Centre for Structural Biology, Department of Life Sciences, Imperial College London, South Kensington, London, United Kingdom.
authors.forename: Mamou
authors.initials: M
authors.lastname: Diallo
authors.affiliation: Centre for Structural Biology, Department of Life Sciences, Imperial College London, South Kensington, London, United Kingdom.
authors.forename: Yingqi
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Centre for Structural Biology, Department of Life Sciences, Imperial College London, South Kensington, London, United Kingdom.
authors.forename: Steve J
authors.initials: SJ
authors.lastname: Matthews
authors.affiliation: Department of Chemistry, University of Turku, Turku, JBL, Arcanum, Turku, Finland.
authors.forename: Anton V
authors.initials: AV
authors.lastname: Zavialov
mesh_terms: D040981:Acinetobacter baumannii / Q000378:metabolism*; D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray / Q000379:methods; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D036781:Fimbriae Proteins / Q000378:metabolism*; D010861:Fimbriae, Bacterial / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D010802:Phylogeny; D021122:Protein Subunits / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D018832:Molecular Chaperones; D021122:Protein Subunits; D036781:Fimbriae Proteins