The Pix pilus adhesin of the uropathogenic Escherichia coli strain X2194 (O2 : K− : H6) is related to Pap pili but exhibits a truncated regulatory region

Abstract

Adhesins provide a major advantage for uropathogenic Escherichia coli in establishing urinary tract infections (UTIs). A novel gene cluster responsible for the expression of a filamentous adhesin of the pyelonephritogenic E. coli strain X2194 has been identified, molecularly cloned, and characterized. The ‘pix operon’ contains eight open reading frames which exhibit significant sequence homology to corresponding genes in the pap operon encoding P pili, the prevalent E. coli adhesins in non-obstructive acute pyelonephritis in humans. Although a pixB gene corresponding to the PapB regulator was identified, a papI homologue could not be found in the pix operon. Instead, a fragment of the R6 gene of the highly uropathogenic E. coli strain CFT073 was identified upstream of pixB. The R6 gene is located in a pathogenicity island containing several pilus-encoding sequences and shows homology to a transposase of Chelatobacter heintzii. In a pixA–lacZ fusion system it was demonstrated that the expression of Pix pili is regulated at the transcriptional level by the R6 gene sequence. A significantly reduced transcription was observed by deleting this fragment and by lowering the growth temperature from 37 to 26 °C. In contrast to other filamentous adhesin systems, Pix pili are mainly expressed in the steady state growth phase and were not repressed by the addition of glucose.

The Pathogenicity Island-Associated K15 Capsule Determinant Exhibits a Novel Genetic Structure and Correlates with Virulence in Uropathogenic Escherichia coli Strain 536

“…In this study, the genetic organization of PAI V 536 was characterized and prominent gene clusters of this PAI have been subjected to functional characterization. The composite PAI V 536 exhibits typical features of PAIs, such as (i) the association with a tRNA-encoding gene, (ii) the presence of different virulence-associated genes (the pix fimbria determinant [33] and the K15 capsule-encoding gene cluster), and (iii) the presence of DR structures formed by the last 22 bp of the 3Ј end of pheV and its truncated copy ЈpheV. Similarly, PAI III 536 also represents a composite island with flanking DR structures formed by the last 47 bp of the 3Ј end of thrW and its truncated copy ЈthrW (16).…”

“…PAI V 536 exhibits typical features of a PAI, e.g., a mosaic-like structure and the presence of multiple functional and fragmented mobile genetic elements. Several virulence-associated factors are encoded on this PAI, including the K15 capsule (ORF60 to 74), the recently described Pix fimbria-encoding gene cluster (ORF6 to 13) which belongs to the P adhesin family (33), and an autotransporter protein (ORF48) with the highest similarity to Sap, a putative autotransporter adhesin encoded on the she PAI of S. flexneri (GenBank accession no. AF326777 and AAL08472) (32).…”

A Conserved PapB Family Member, TosR, Regulates Expression of the Uropathogenic Escherichia coli RTX Nonfimbrial Adhesin TosA while Conserved LuxR Family Members TosE and TosF Suppress Motility

“…Minor groove binding proteins often take advantage of the inherent DNA structure of AT-rich regions to mediate target recognition and binding (66)(67)(68)(69), which is likely the case for PapB family members (61)(62)(63). Indeed, the region upstream of the tos operon, which contains the tos promoter, is an AT-rich sequence.…”

“…The sequence immediately upstream of a gene encoding a PapB family member is often AT rich (61,62), and tandem repeated AT-rich nonomers often demarcate PapB family member binding sites (61,63). Indeed, the region immediately upstream of tosR is AT rich (Fig.…”

Evolution of the Chaperone/Usher Assembly Pathway: Fimbrial Classification Goes Greek

“…While PapD is the periplasmic chaperone for the P-fimbrial subunits (25,186,306,365), PapJ plays an auxiliary role by ensuring the proper integration of PapA into the fimbrial shaft (326). E. coli fimbrial operons that are closely related to pap include prf (P-related fimbriae) (226), pix (Pix fimbriae) (206), and sfp (Sfp fimbriae) (44). While P-related fimbriae and Pix fimbriae are morphologically similar to P fimbriae, Sfp fimbriae are only 3 to 5 nm in diameter (44).…”