Discovery of Intracellular Heme-binding Protein HrtR, Which Controls Heme Efflux by the Conserved HrtB-HrtA Transporter in Lactococcus lactis

Structural Basis for the Transcriptional Regulation of Heme Homeostasis in Lactococcus lactis

“…3, MBP fused to the N terminus may interfere with the interaction between the ␣3 helix and the target DNA by steric hindrance and/or perturbation of the conformation of the DNA-binding domain. As wild-type MBP-HrtR, however, shows formation of the MBP-HrtR⅐DNA complex (15), the reasons for this discrepancy remain unclear for the DNA binding ability of H72A and H149L variants.…”

“…Although numerous lactic acid bacteria, including L. lactis, acquire heme molecules exogenously to establish an aerobic respiratory chain, they cannot biosynthesize heme molecules due to the lack of the enzymes for heme biosynthesis. Although the regulation of efflux of excess heme molecules out of an L. lactis cell is reported to be the key process to maintain heme homeostasis in L. lactis, the detailed regulatory mechanism remains to be elucidated (10,15). In this study, we have elucidated the molecular mechanisms of heme-responsive transcriptional regulation for the heme-efflux system in L. lactis based on the crystal structures of the heme-sensing transcriptional regulator HrtR.…”

The two-component system ChrSA is crucial for haem tolerance and interferes with HrrSA in haem-dependent gene regulation in Corynebacterium glutamicum

“…An alternative regulatory mechanism of transcriptional regulation of hrtBA has recently been reported for the Gram-positive commensal bacterium Lactococcus lactis. Here, the cytoplasmic onecomponent regulator HrtR was described as a crucial factor for the haem-dependent activation of hrtBA (Lechardeur et al, 2012). This mechanism is conserved among different Gram-positive commensals and contrasts with the TCSmediated control described for several pathogenic species as well as C. glutamicum.…”

The TetR Family of Regulators

“…L. lactis does not synthesize heme. HrtR senses intracellular heme and regulates expression of a heme exporter encoded by HrtBA (191).…”