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

An important Salmonella serovar for both human and animals Salmonella Typhimurium possesses 13 gene clusters that have the potential to produce fimbrial structure, among which the type 1 fimbriae with the binding specificity to mannose residue is the most commonly found type. Six structural genes and five regulatory genes comprise the fim gene cluster that is responsible for the production of type 1 fimbriae in S. Typhimurium. The fimY gene encodes a positive regulator for type 1 fimbrial expression since a deletion in fimY abolished the production of fimbriae. The N‐terminal portion of FimY contains amino acid residues that exhibit some similarity as those found in the proteins possessing the PilZ domain, which is engaged in cyclic di‐GMP binding. A fimY allele that had a change from arginine to alanine at position 7 (R7A) or 7 and 11 (R7/11A) generated by site‐directed mutagenesis in a (6)RRERH(11)R motif near N‐terminal, when cloned in pACYC184 and transformed into a fimY‐deleted strain, decreased the expression of fimA and fimZ. The number of type 1 fimbriae in these two transformants was also less than those of the other transformants that contained different fimY alleles in pACYC184 when observed in electron microscopy. However, changing from arginine to alanine at position 11 (R11A) remained the same as the wild‐type fimY allele. It is likely that the arginine at the 7th position of FimY is critical for its maximal activating activity upon fimZ. Another motif (83)DI(85)SLWIEK(91)G motif did not affect the function of FimY. Although FimY has the two aforementioned motifs, which contain some amino acids that are present within those of the PilZ domain proteins, secondary structure prediction analysis did not reveal that FimY has a conformation commonly observed in PilZ‐like proteins. Therefore, FimY and PilZ domain proteins are not homologs. Further investigation for a detailed analysis of FimY is thus warranted.