Transcriptional Regulation of the 4-Amino-4-deoxy-L-arabinose Biosynthetic Genes in Yersinia pestis

Mollie D Winfield,Tammy Latifi,Eduardo A Groisman

doi:10.1074/jbc.m413900200

Mollie D Winfield, Tammy Latifi + Show 1 more

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https://doi.org/10.1074/jbc.m413900200

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Abstract

Inducible membrane remodeling is an adaptive mechanism that enables Gram-negative bacteria to resist killing by cationic antimicrobial peptides and to avoid eliciting an immune response. Addition of 4-amino-4-deoxy-l -arabinose (4-aminoarabinose) moieties to the phosphate residues of the lipid A portion of the lipopolysaccharide decreases the net negative charge of the bacterial membrane resulting in protection from the cationic antimicrobial peptide polymyxin B. In Salmonella enterica serovar Typhimurium, the PmrA/PmrB two-component regulatory system governs resistance to polymyxin B by controlling transcription of the 4-aminoarabinose biosynthetic genes. Transcription of PmrA-activated genes is induced by Fe(3+), which is sensed by PmrA cognate sensor PmrB, and by low Mg(2+), in a mechanism that requires not only the PmrA and PmrB proteins but also the Mg(2+)-responding PhoP/PhoQ system and the PhoP-activated PmrD protein, a post-translational activator of the PmrA protein. Surprisingly, Yersinia pestis can promote PhoP-dependent modification of its lipid A with 4-aminoarabinose despite lacking a PmrD protein. Here we report that Yersinia uses different promoters to transcribe the 4-aminoarabinose biosynthetic genes pbgP and ugd depending on the inducing signal. This is accomplished by the presence of distinct binding sites for the PmrA and PhoP proteins in the promoters of the pbgP and ugd genes. Our results demonstrate that closely related bacterial species may use disparate regulatory pathways to control genes encoding conserved proteins.

Highlights

The lipopolysaccharide (LPS)1 is a major component of the outer membrane of Gram-negative bacteria [1, 2]
Because Y. pestis harbors a Mg2ϩ-responsive PhoP/PhoQ system [48], can modify its lipid A with 4-aminoarabinose in a PhoPdependent manner [14], and encodes a conserved PmrA/PmrB system [37, 47], we reasoned that the low Mg2ϩ induction of the 4-aminoarabinose biosynthetic genes taking place in Yersinia must involve a mechanism different from the PmrD-dependent pathway described in Salmonella [27, 28] (Fig. 1A)
We identified two transcription start sites: an ORF-proximal site that was stronger in organisms experiencing low Mg2ϩ than in those exposed to low Mg2ϩ ϩ Fe3ϩ, and an ORF-distal site that displayed the opposite behavior (Fig. 2A)

Summary

Introduction

The lipopolysaccharide (LPS) is a major component of the outer membrane of Gram-negative bacteria [1, 2]. Salmonella modifies its lipid A with 4-aminoarabinose during infection of murine macrophages [33] This modification appears to be PhoP/PhoQ-dependent because it was detected only under PhoP-inducing conditions when bacteria were grown in defined media [33], and because expression of the ugd gene inside macrophages required a functional PhoP/PhoQ system even though ugd transcription can be promoted by other two-component systems independently of PhoP/PhoQ [34]. The plague agent Yersinia pestis can promote PhoP-dependent modification of its LPS with 4-aminoarabinose [14] This is surprising because Yersinia lacks a PmrD protein. It indicates that Salmonella and Yersinia must use different strategies to promote expression of lipid A modifying genes under PhoP-inducing conditions. We report the mechanism by which Y. pestis regulates expression of the 4-amino-

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