Characterization of FimY as a Coactivator of Type 1 Fimbrial Expression in Salmonella enterica Serovar Typhimurium

Abstract

Type 1 fimbriae of Salmonella enterica serovar Typhimurium are surface appendages that carry adhesins specific for mannosylated host glycoconjugates. Regulation of the major fimbrial subunit is thought to be controlled by a number of ancillary fim genes, including fimZ, fimY, fimW, and fimU. Previous studies using a FimZ mutant have indicated that this protein is necessary for fimA expression, and in vitro DNA binding assays determined that FimZ is a transcriptional activator that binds directly to the fimA promoter. To determine the role of FimY as a potential regulator of fimbrial expression, a fimY mutant of serovar Typhimurium was generated by allelic exchange. This mutant was found to be phenotypically nonfimbriate. No transcription from the fimA promoter was detected in a fimY mutant containing a fimA-lacZ reporter construct located on the chromosome. In addition, transcription from the cloned fimY promoter was not detected in Escherichia coli unless both FimZ and FimY were present, indicating that these proteins also act as coactivators of fimY expression. Consistent with these results, there is no transcription from a fimY-lacZ reporter construct within a serovar Typhimurium fimY or fimZ mutant. Studies using the fimY-lacZ construct reveal that expression of this gene varies with environmental conditions in a manner similar to fimA expression. Extensive in vitro DNA binding assays using extracts from E. coli that overexpress FimY, as well as partially purified FimY, were unable to identify a specific interaction between FimY and the fimA or fimY promoter. The results indicate that FimY is a positive regulator of fimbrial expression and that this protein acts in cooperation with FimZ to regulate the expression of Salmonella type 1 fimbrial appendages.

Genomic analysis and growth-phase-dependent regulation of the SEF14 fimbriae of Salmonella enterica serovar Enteritidis The GenBank accession number for the sequence reported in this paper is AF239978.

“…Although many other fimbrial systems from Salmonella serovars have been identified and characterized, type I fimbriae and the aggregative fimbriae encoded by agfBAC were the only examples for which a transcriptional regulator has been identified (Romling et al, 2000 ;Tinker & Clegg, 2000. It remains to be seen which elements are required for these systems.…”

Role of MrkJ, a Phosphodiesterase, in Type 3 Fimbrial Expression and Biofilm Formation in Klebsiella pneumoniae

“…For example, the gene encoding E. coli type 1 pili is regulated by the fimS invertible switch that, depending upon its orientation, controls the transcription of fimA (16,41). In Salmonella spp., however, fimA is regulated by at least two activators (fimZ and fimY) and one repressor (fimW), with FimZ being a DNA-binding protein (46,47,49). The E. coli P pili and Salmonella Pef pili are also regulated by the production of DNA-binding proteins that are distinct from those associated with the type 1 fimbriae (2,5,33).…”

The Leucine-Responsive Regulatory Protein, Lrp, Activates Transcription of thefimOperon inSalmonella entericaSerovar Typhimurium via thefimZRegulatory Gene

“…The FimZ protein is an "orphan" member of the response regulator family of transcription factors, that is, one for whom no cognate histidine protein kinase partner has been identified (83,84). The FimY protein is an essential coregulator that cooperates with FimZ in activating the fimA promoter through a mechanism that does not involve a direct interaction between FimY and fimA (72). A third regulatory protein, FimW, exerts a negative effect on fimA expression through a FimW-FimZ protein-protein interaction that is inhibitory toward the positive influence of the FimZ protein (74).…”