FimY of Salmonella enterica serovar Typhimurium functions as a DNA-binding protein and binds the fimZ promoter

Abstract

Salmonella enterica serovar Typhimurium produces type 1 fimbriae with binding specificity to mannose residues. Elements involved in fimbrial structural biosynthesis, transport, and regulation are encoded by the fim gene cluster. FimZ, FimY, FimW, STM0551, and an arginine transfer RNA (fimU) were previously demonstrated to regulate fimbrial expression. The amino acid sequences of the C-terminal portion of FimY revealed similarity with those of LuxR-like proteins. Electrophoretic mobility shift assays indicated that FimY possessed DNA-binding capacity and bound a 605-bp DNA fragment spanning the intergenic region between fimY and fimZ, while a FimY protein harboring a double mutation in the C-terminal helix-turn-helix region containing a glycine (G) to aspartate (D) substitution at residue 189 and isoleucine (I) to lysine (K) substitution at residue 195 lost its ability to bind this DNA fragment. A lux box sequence (5'-TCTGTTATTACATAACAAATACT-3') within the fimZ promoter was required for binding. None of the DNA fragments derived from the promoters for fimA, fimY, or fimW was shifted by FimY. Pull-down assays showed that there were physical protein/protein interactions between FimY and FimZ. We propose that in the regulatory circuit of type 1 fimbriae, FimY functions as a DNA-binding protein to activate fimZ, and a FimY-FimZ protein complex may form to regulate other fim genes. Confirming these proposals requires further study.

Arginine within a specific motif near the N‐terminal of FimY is critical for the maximal production of type 1 fimbriae in Salmonella enterica serovar Typhimurium

“…In the regulatory network of type 1 fimbriae in S . typhimurium , fimY may act upstream of fimZ ; that is to say, fimY activates fimZ , and in turn fimZ activates fimA , resulting in the production of fimbriae (Wang et al, ; Zeiner, ). Many fimY transcripts in Δ fimY ( fimY ) strain should be responsible for the mass production of fimA through the fimY→fimZ→fimA pathway, leading to a high agglutination titer.…”

“…The reason that ΔfimY (fimY ) strain exhibited a higher agglutination titer than that of the wild-type strain (4.64 vs. 2.75) may be due to the copy number effect of the pACYC184. In the regulatory network of type 1 fimbriae in S. typhimurium, fimY may act upstream of fimZ; that is to say, fimY activates fimZ, and in turn fimZ activates fimA, resulting in the production of fimbriae (Wang et al, 2014;Zeiner, 2012). Many fimY transcripts in ΔfimY (fimY ) strain should be responsible for the mass production of fimA through the fimY→fimZ→fimA pathway, leading to a high agglutination titer.…”

“…FimY is a positive regulator for type 1 fimbrial expression in S. Typhimurium. The C-terminal part of FimY possesses a helixturn-helix motif and FimY was shown to bind to the promoter region of fimZ (Wang, Hsu, Huang, Lin, & Yeh, 2014); however, some aspects of its mechanism in terms of fimbrial regulation remains to be elucidated. For example, the members of the PilZ family regulator, such as YcgR of Escherichia coli and MrkH of Klebsiella pneumoniae (Ryjenkov, Simm, Romling, & Gomelsky, 2006;Wilksch et al, 2011), often contain two conserved domains RRxxxR and DxSxxG (x designates any amino acid), which involve in binding cyclic di-GMP (c-di-GMP), a second messenger that controls many physiological processes of bacteria (Jenal, Reinders, & Lori, 2017).…”

Salmonella Fimbriae: What is the Clue to Their Hairdo?

“…This cluster is the most studied and one of the most conserved fimbriae of Salmonella enterica and was mainly characterised in S. Typhimurium. These fimbriae have a binding specificity for mannose residues [63]. The fim fimbria of Salmonella is not homologue with its homonym from E. coli, except for sharing some morphological and [64,65].…”

“…FimY upregulates fimZ expression by binding to the fimZ promoter. FimY and FimZ then form a complex that activates the fimA promoter [63,69]; fimY is itself regulated by the arginine tRNA fimU [72]. Lrp is another regulator that binds and activates the fimZ promoter, probably by antagonising the binding of the global repressor protein H-NS to this promoter region [67,70,73].…”