Abstract
Peroxide sensing is essential for bacterial survival during aerobic metabolism and host infection. Peroxide stress regulators (PerRs) are homodimeric transcriptional repressors with each monomer typically containing both structural and regulatory metal-binding sites. PerR binding to gene promoters is controlled by the presence of iron in the regulatory site, and iron-catalyzed oxidation of PerR by H2O2 leads to the dissociation of PerR from DNA. In addition to a regulatory metal, most PerRs require a structural metal for proper dimeric assembly. We present here a structural and functional characterization of the PerR from the pathogenic spirochete Leptospira interrogans, a rare example of PerR lacking a structural metal-binding site. In vivo studies showed that the leptospiral PerR belongs to the peroxide stimulon in pathogenic species and is involved in controlling resistance to peroxide. Moreover, a perR mutant had decreased fitness in other host-related stress conditions, including at 37 °C or in the presence of superoxide anion. In vitro, leptospiral PerR could bind to the perR promoter region in a metal-dependent manner. The crystal structure of the leptospiral PerR revealed an asymmetric homodimer, with one monomer displaying complete regulatory metal coordination in the characteristic caliper-like DNA-binding conformation and the second monomer exhibiting disrupted regulatory metal coordination in an open non-DNA-binding conformation. This structure showed that leptospiral PerR assembles into a dimer in which a metal-induced conformational switch can occur independently in the two monomers. Our study demonstrates that structural metal binding is not compulsory for PerR dimeric assembly and for regulating peroxide stress.
Highlights
We show that the binding of Leptospira interrogans Peroxide stress regulators (PerRs) with its promoter region is metal-dependent, and we report the crystal structure of the homodimeric PerR from L. interrogans, which provides a snapshot of the metal-induced conformational switch required for DNA binding and dissociation
Leptospira spp. encode a PerR ORF that shares about 30% amino acid identity with PerRs encoded by other bacteria (Campylobacter jejuni, B. subtilis, Staphylococcus aureus, and Streptococcus pyogenes) (Fig. S1A)
Crystal structures have been reported for PerRs from only two bacteria, B. subtilis and S. pyogenes [6, 8, 10, 26, 27]
Summary
Leptospira are among the few examples of Gram-negative bacteria that possess a PerR-like regulator involved in controlling defenses against peroxide stress [12]. These aerobic bacteria of the spirochetal phylum have pathogenic representatives that are the causative agents of leptospirosis, a widespread zoonotic disease [13, 14]. Catalase is required for survival in the presence of H2O2 and for virulence [24], and perR is up-regulated when cells are grown in rats [25] These findings strongly suggest a role of PerR in the adaptation of pathogenic Leptospira to a mammalian host. We have investigated the effect of perR inactivation on the growth of Leptospira in conditions similar to those encountered in a mammalian host
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