The Escherichia coli P and Type 1 Pilus Assembly Chaperones PapD and FimC Are Monomeric in Solution

Abstract

The chaperone/usher pathway is used by Gram-negative bacteria to assemble adhesive surface structures known as pili or fimbriae. Uropathogenic strains of Escherichia coli use this pathway to assemble P and type 1 pili, which facilitate colonization of the kidney and bladder, respectively. Pilus assembly requires a periplasmic chaperone and outer membrane protein termed the usher. The chaperone allows folding of pilus subunits and escorts the subunits to the usher for polymerization into pili and secretion to the cell surface. Based on previous structures of mutant versions of the P pilus chaperone PapD, it was suggested that the chaperone dimerizes in the periplasm as a self-capping mechanism. Such dimerization is counterintuitive because the chaperone G1 strand, important for chaperone-subunit interaction, is buried at the dimer interface. Here, we show that the wild-type PapD chaperone also forms a dimer in the crystal lattice; however, the dimer interface is different from the previously solved structures. In contrast to the crystal structures, we found that both PapD and the type 1 pilus chaperone, FimC, are monomeric in solution. Our findings indicate that pilus chaperones do not sequester their G1 ␤-strand by forming a dimer. Instead, the chaperones may expose their G1 strand for facile interaction with pilus subunits. We also found that the type 1 pilus adhesin, FimH, is flexible in solution while in complex with its chaperone, whereas the P pilus adhesin, PapGII, is rigid. Our study clarifies a crucial step in pilus biogenesis and reveals pilus-specific differences that may relate to biological function. IMPORTANCEPili are critical virulence factors for many bacterial pathogens. Uropathogenic E. coli relies on P and type 1 pili assembled by the chaperone/usher pathway to adhere to the urinary tract and establish infection. Studying pilus assembly is important for understanding mechanisms of protein secretion, as well as for identifying points for therapeutic intervention. Pilus biogenesis is a multistep process. This work investigates the oligomeric state of the pilus chaperone in the periplasm, which is important for understanding early assembly events. Our work unambiguously demonstrates that both PapD and FimC chaperones are monomeric in solution. We further demonstrate that the solution behavior of the FimH and PapGII adhesins differ, which may be related to functional differences between the two pilus systems.A n important step in the pathogenesis of uropathogenic Escherichia coli is the binding to host receptors within the urinary tract. This is accomplished by the recognition of sugar moieties on the surface of urothelial cells by lectins at the tip of elongated organelles, termed pili or fimbriae (1, 2). Specifically, uropathogenic E. coli expresses type 1 and P pili, which mediate binding to the bladder and kidney, respectively (3, 4). Type 1 and P pili are assembled by the chaperone/usher pathway, which is a conserved secretion system used to assemble a wide variety of pilus-type struct...

Urinary Tract Infections Caused by Uropathogenic Escherichia coli: Mechanisms of Infection and Treatment Options

“…Furthermore, they can be up to 2 μm in length and 10 nm in width, which guarantees successful bacterial attachment. Meanwhile, numerous studies have found that over 50% of women with an acute UTI show strong positive type 1 fimbriae via the immunostaining of urine sediments [ 44 ], with results comparable to those obtained in acutely infected mice [ 45 ]. Interestingly, a study found that urine decreases the UPEC expression of type 1 fimbriae [ 46 , 47 ], which may explain the results above.…”

Distribution of Pathogenicity Islands Among Uropathogenic Escherichia coli Isolates From Patients With Urinary Tract Infections

“…PAI IIJ96 contains a hly operon, as well as a prs operon encoding a different class of pilus and a gene encoding the cytotoxic necrotizing factor 1 (CNF1). [6][7][8] PAI ICFT073, which carries an Alpha-hemolysin operon (hly), a pap operon encoding P-fimbriae, aerobactin, and genes related to iron transport systems and putative carbohydrate transport systems. 9 PAI IICFT073 contains a pap operon, iron-regulated genes, mobile genetic elements, and a large number of unknown genes.…”

A review on pilus assembly mechanisms in Gram-positive and Gram-negative bacteria

“… ( Walczak et al, 2014 ) FimC Chaperone donates its strand to upcoming pili during pili polymerization. ( Sarowar et al, 2016 ) FimD Usher pathway, transfers the pilin subunits from periplasm to outer membrane. ( Sarowar et al, 2016 ) FimF, G The adapter subunit, holds the pilin subunits.…”

“… ( Sarowar et al, 2016 ) FimD Usher pathway, transfers the pilin subunits from periplasm to outer membrane. ( Sarowar et al, 2016 ) FimF, G The adapter subunit, holds the pilin subunits. ( Busch et al, 2015 ) FimH Tip pilin, mediates the host-pathogen interaction.…”