Zinc is an inhibitor of the LdtR transcriptional activator

Abstract

LdtR is a master regulator of gene expression in Liberibacter asiaticus, one of the causative agents of citrus greening disease. LdtR belongs to the MarR-family of transcriptional regulators and it has been linked to the regulation of more than 180 genes in Liberibacter species, most of them gathered in the following Clusters of Orthologous Groups: cell motility, cell wall envelope, energy production, and transcription. Our previous transcriptomic evidence suggested that LdtR is directly involved in the modulation of the zinc uptake system genes (znu) in the closely related L. crescens. In this report, we show that LdtR is involved in the regulation of one of the two encoded zinc uptake mechanisms in L. asiaticus, named znu2. We also show that LdtR binds zinc with higher affinity than benzbromarone, a synthetic effector inhibitory molecule, resulting in the disruption of the LdtR:promoter interactions. Using site-directed mutagenesis, electrophoretic mobility shift assays (EMSAs), and isothermal titration calorimetry, we identified that residues C28 and T43 in LdtR, located in close proximity to the Benz1 pocket, are involved in the interaction with zinc. These results provided new evidence of a high-affinity effector molecule targeting a key player in L. asiaticus’ physiology and complemented our previous findings about the mechanisms of signal transduction in members of the MarR-family.

Osmotic stress induces long-term biofilm survival in Liberibacter crescens

“…Increments in the D-methionine pool, and perhaps the L- enantiomer too, may be involved in the strengthening of the cell wall in L. crescens as a response to heat stress. The zinc/manganese ABC transporter systems znu 2 and znu 3 [ 19 ] were up-regulated under heat stress. In our previous transcriptomic analysis, where LdtR was chemically inhibited, we observed up-regulation of the znu 3 system, but down-regulation of the znu 2 system [ 20 ], which suggest these genes possess more than one regulatory mechanism.…”

“…We identified LdtR as a global regulator involved in osmotic stress response in L . asiaticus , L. crescens , and Sinorhirobium meliloti [ 16 – 19 ]. LdtR is a member of the MarR-family of transcriptional regulators and was found to control the expression of more than 180 genes in L .…”

MarR family proteins sense sulfane sulfur in bacteria

“…LdtR tightly binds Zn 2+ with Cys28 and Thr43, the two key residues located near the junction between the dimerization and DNA‐binding domains. The binding results in a conformational change of LdtR, disrupting the binding of LdtR to the operator and inducing the expression of various genes 63 . Thus, the binding of Zn 2+ leads to different outcomes for AdcR and LdtR.…”