PNNL

Abstract

The surfaces of many bacteria feature pili or fimbriae, proteinaceous filaments that play an integral role in the adhesion of bacteria to host cells and, hence, in their pathogenicity.1,2 These extracellular structures are key virulence factors and potential targets for antibacterial drug and vaccine development. In certain Salmonella enterobacteria strains, one such class of fimbriae, the virulence plasmid-encoded fimbriae encoded by the pef operon,3,4 has been shown to be important for adhesion to murine small intestine and fluid accumulation.5 Although regulation of fimbrial expression is complex, transcription of the pef operon, induced under acidic conditions, is modulated by the PefI regulatory protein.6 PefI represses plasmid-encoded fimbrial protein production by activating the leucine-responsive regulatory protein (Lrp) mediated inhibition of DNA methylation within the pef promoter region.6 PefI expression also inhibits transcription of flagellar proteins and consequently cell motility.7 Here we present the solution NMR structure of the 70-residue PefI transcription regulator from Salmonella enterica serovar Typhimurium LT2 [UniProtKB/TrEMBL ID, Q04822_SALTY; NESG ID, StR82; hereafter referred to as stPefI], a member of the FaeA-like protein domain family (Pfam identifier, PF04703). The sequence alignment of stPefI with its functional homolog in Escherichia coli, PapI, is shown in Fig. 1(A). We demonstrate that the structure of stPefI adopts a winged helix-turn-helix motif,8,9 consistent with its role as a DNA-binding transcriptional regulator. Moreover, in spite of their relatively low sequence identity (29%), the structure of stPefI is highly similar to that of E. coli PapI,10 which activates the expression of pyelonephritis-associated pili.11,12