SirR, a Novel Iron-Dependent Repressor in Staphylococcus epidermidis

Abstract

In Staphylococcus epidermidis and Staphylococcus aureus, a number of cell wall-and cytoplasmic membraneassociated lipoproteins are induced in response to iron starvation. To gain insights into the molecular basis of iron-dependent gene regulation in the staphylococci, we sequenced the DNA upstream of the 3-kb S. epidermidis sitABC operon, which Northern blot analysis indicates is transcriptionally regulated by the growth medium iron content. We identified two DNA sequences which are homologous to elements of the Corynebacterium diphtheriae DtxR regulon, which controls, in response to iron stress, for example, production of diphtheria toxin, siderophore, and a heme oxygenase. Upstream of the sitABC operon and divergently transcribed lies a 645-bp open reading frame (ORF), which codes for a polypeptide of approximately 25 kDa with homology to the DtxR family of metal-dependent repressor proteins. This ORF has been designated SirR (staphylococcal iron regulator repressor). Within the sitABC promoter/operator region, we also located a region of dyad symmetry overlapping the transcriptional start of sitABC which shows high homology to the DtxR operator consensus sequence, suggesting that this region, termed the Sir box, is the SirR-binding site. The SirR protein was overexpressed, purified, and used in DNA mobility shift assays; SirR retarded the migration of a synthetic oligonucleotide based on the Sir box in a metal (Fe 2؉ or Mn 2؉ )-dependent manner, providing confirmatory evidence that this motif is the SirR-binding site. Furthermore, Southern blot analysis of staphylococcal chromosomal DNA with the synthetic Sir box as a probe confirmed that there are at least five Sir boxes in the S. epidermidis genome and at least three in the genome of S. aureus, suggesting that SirR controls the expression of multiple target genes. Using a monospecific polyclonal antibody raised against SirR to probe Western blots of whole-cell lysates of S. aureus, S. carnosus, S. epidermidis, S. hominis, S. cohnii, S. lugdunensis, and S. haemolyticus, we identified an approximately 25-kDa cross-reactive protein in each of the staphylococcal species examined. Taken together, these data suggest that SirR functions as a divalent metal cation-dependent transcriptional repressor which is widespread among the staphylococci.

Functional analysis of two divalent metal‐dependent regulatory genes dmdR1 and dmdR2 in Streptomyces coelicolor and proteome changes in deletion mutants

“…[10], indicates that the dmdR family of iron (or other divalent metals) regulatory proteins is common in Gram-positive bacteria [13]. A related protein family, SirR, occurs in Staphylococcus epidermidis [20]. A detailed analysis of the amino acid sequences of the DmdR1 and DmdR2 proteins in comparison with those of other actinomycetes revealed a strong conservation of motifs in domains 1 and 2 ( 70% identical residues), particularly in the DNA-binding region (domain 1) which contains an HTH motif [21] and the metal-binding and dimerization domains (domain 2) [22,23].…”

Regulation of catalase–peroxidase (KatG) expression, isoniazid sensitivity and virulence by furA of Mycobacterium tuberculosis

“…This is compatible with the presence of the gene ideR in M. tuberculosis, which has been shown to act as a repressor of exochelin and mycobactin synthesis in M. smegmatis (Dussurget et al, 1996), although the ideR mutant of M. smegmatis did not have complete derepression of siderophore synthesis in iron-rich conditions, suggesting the presence of a second iron-dependent repressor in mycobacteria. FurB, which is more closely related to E. coli Fur than FurA, or the gene Rv2788, which has similarity to an iron-dependent regulator SirR from Staphylococcus epidermis (Hill et al, 1998), are two possible candidates for this second repressor (De Voss et al, 1999).…”

Iron and heme utilization inPorphyromonas gingivalis

“…This protein shows homology to FeoA, a protein involved in Fe 2+ transport in other bacteria [219]. It is also similar to iron dependent repressors that include the diphteria toxin repressor DtxR from Corynebacterium species [220], and transcriptional repressor SirR from Staphylococcus species [221].…”