Distinct Residues Contribute to Motility Repression and Autoregulation in the Proteus mirabilis Fimbria-Associated Transcriptional Regulator AtfJ

Abstract

Proteus mirabilis contributes to a significant number of catheter-associated urinary tract infections, where coordinated regulation of adherence and motility is critical for ascending disease progression. Previously, the mannose-resistant Proteus-like (MR/P) fimbria-associated transcriptional regulator MrpJ has been shown to both repress motility and directly induce the transcription of its own operon; in addition, it affects the expression of a wide range of cellular processes. Interestingly, 14 additional mrpJ paralogs are included in the P. mirabilis genome. Looking at a selection of MrpJ paralogs, we discovered that these proteins, which consistently repress motility, also have nonidentical functions that include cross-regulation of fimbrial operons. A subset of paralogs, including AtfJ (encoded by the ambient temperature fimbrial operon), Fim8J, and MrpJ, are capable of autoinduction. We identified an element of the atf promoter extending from 487 to 655 nucleotides upstream of the transcriptional start site that is responsive to AtfJ, and we found that AtfJ directly binds this fragment. Mutational analysis of AtfJ revealed that its two identified functions, autoregulation and motility repression, are not invariably linked. Residues within the DNA-binding helix-turn-helix domain are required for motility repression but not necessarily autoregulation. Likewise, the C-terminal domain is dispensable for motility repression but is essential for autoregulation. Supported by a three-dimensional (3D) structural model, we hypothesize that the C-terminal domain confers unique regulatory capacities on the AtfJ family of regulators. IMPORTANCEBalancing adherence with motility is essential for uropathogens to successfully establish a foothold in their host. Proteus mirabilis uses a fimbria-associated transcriptional regulator to switch between these antagonistic processes by increasing fimbrial adherence while simultaneously downregulating flagella. The discovery of multiple related proteins, many of which also function as motility repressors, encoded in the P. mirabilis genome has raised considerable interest as to their functionality and potential redundancy in this organism. This study provides an important advance in this field by elucidating the nonidentical effects of these paralogs on a molecular level. Our mechanistic studies of one member of this group, AtfJ, shed light on how these differing functions may be conferred despite the limited sequence variety exhibited by the paralogous proteins.T ranscriptional regulation in response to environmental cues, including temperature and nutrient availability, is critical to allow bacteria to adapt to their surroundings. The advent of whole-genome sequencing has led to the discovery that some pathogenic bacteria devote as much as 10% of their genome to regulatory systems, such as transcription factors, allowing for the appropriate protective or adaptive response to new environments (1, 2).Urinary tract pathogens, such as the Gram-negative enterobacterium Proteu...

Pathogenesis of Proteus mirabilis Infection

“…Notably, MrpJ paralogs are not restricted to P. mirabilis as they have been detected in fimbrial operons from related genera (264–266). Because fimbriae allow bacteria to adhere or form biofilms in specific environments, and thus respond to niche-specific signals, MrpJ paralogs have been proposed to orchestrate genetic programs that are beneficial to those environments (132, 267). …”

“…Like MrpJ itself, the MrpJ paralogs regulate other fimbrial operons in addition to repressing motility (267). Screening of MrpJ, UcaJ, AtfJ, and Fim8J showed that some paralogs positively auto-regulate their operons.…”

“…Screening of MrpJ, UcaJ, AtfJ, and Fim8J showed that some paralogs positively auto-regulate their operons. Strikingly, AtfA and Fim8A strongly induced their respective operons while having modest or no effects on other fimbrial genes ( mrpA , ucaA , or pmfA ); in contrast, UcaJ has no effect on the uca operon (267). Examination of the atf promoter using deletion analysis indicated that AtfJ interacts with a region 486 to 655 bp upstream of the transcriptional start site (267).…”

“…Strikingly, AtfA and Fim8A strongly induced their respective operons while having modest or no effects on other fimbrial genes ( mrpA , ucaA , or pmfA ); in contrast, UcaJ has no effect on the uca operon (267). Examination of the atf promoter using deletion analysis indicated that AtfJ interacts with a region 486 to 655 bp upstream of the transcriptional start site (267). Thus, other MrpJ paralogs may share a common feature of binding DNA far away from transcriptional machinery binding sites.…”

“…Thus, other MrpJ paralogs may share a common feature of binding DNA far away from transcriptional machinery binding sites. Deletion of the AtfJ C-terminal tail had little effect on motility repression, but was required for atf autoregulation (267). Protein modeling of the AtfJ C-terminus suggests this region is involved in protein-protein interactions, and it has been proposed that MrpJ paralogs exert their unique properties via their divergent C-termini (138, 267).…”